A Review of the Methodology in Studies on the Treatment of the Proximal Interphalangeal Joint to Analyze Homogeneity and Detect Inconsistencies

Abstract

Background/Objectives: The treatment of proximal interphalangeal joint stiffness is challenging due to methodological inconsistencies in existing studies. While many studies report range of motion improvements, their limitations raise concerns about result reliability. This review examines whether studies follow standardized protocols or present inconsistencies that hinder evidence-based clinical recommendations. Methods: A systematic review was conducted following PRISMA 2020 guidelines. A literature search in PubMed, Cochrane, PEDro, and ScienceDirect included randomized controlled trials, observational studies, case reports, and systematic reviews. Study quality was assessed based on design, blinding, data collection, and reporting consistency, focusing on standardized range of motion measurements. Results: Most studies showed significant methodological deficiencies, including a lack of controls, inconsistent outcome measures, small samples, and failure to report essential data such as baseline and final range of motion values with standard deviations. These inconsistencies prevented determination of whether reported improvements were treatment-induced or influenced by external factors. Conclusions: Greater methodological rigor is needed in research on the proximal interphalangeal joint. Without standardized protocols, rigorous data collection, and proper controls, treatment effectiveness cannot be reliably assessed. Future studies must ensure methodological consistency to generate evidence-based recommendations.

1. Introduction

Proximal interphalangeal joint (PIPJ) stiffness is a condition that significantly affects hand function, limiting the ability to perform essential activities and reducing patients’ quality of life (QoL). Its clinical management is complex due to the variety of factors that can contribute to its development, including direct trauma, prolonged immobilization, postoperative complications, and various associated pathologies. These factors progressively reduce the joint’s range of motion (ROM), potentially leading to persistent functional disability and, in advanced cases, permanent deformities [1].

To address this condition, various therapeutic strategies have been developed, which can be broadly categorized into conservative and surgical interventions. Among conservative options, the use of orthoses or splinting is one of the most commonly employed tools in clinical practice, along with other approaches such as therapeutic exercises, manual therapy, and joint mobilization techniques [2,3,4]. Orthoses, in particular, can be classified into static, static progressive, dynamic, and torque transmission devices, each with specific mechanisms of action aimed at promoting joint mobility and preventing stiffness progression [4,5,6].

Within this field, our research group has developed and evaluated digital neoprene orthoses with elastic tension as an alternative for the progressive recovery of joint ROM. Our studies have demonstrated their potential to provide controlled and sustained force, gradually facilitating the extension of the affected joint [7]. These devices have generated increasing interest in clinical practice, as they offer an accessible and less-invasive alternative compared to other interventions. Analyzing their applicability within the broader set of available therapeutic strategies is essential to understanding their impact in various clinical settings.

Despite the growing interest in these strategies, a more in-depth analysis is still needed to understand how they are implemented in clinical practice, the criteria used for their selection, and the methodological frameworks that support their application [8]. Beyond their effectiveness, it is crucial to understand the rationale and methodology behind each intervention to establish a more structured therapeutic approach. In this regard, Harvey [9], in one of the most comprehensive Cochrane systematic reviews on the topic, concluded that stretching does not have clinically relevant effects on joint mobility. This finding underscores the necessity of documenting and analyzing the methodologies used in different therapeutic strategies.

Therefore, the present study aims to examine the current state of knowledge on PIPJ stiffness by documenting existing therapeutic strategies and analyzing the methodological approaches employed in their study. To ensure the quality and reproducibility of findings, this review will adhere to widely recognized methodological standards, such as the PRISMA guidelines, which provide a structured framework for conducting systematic reviews and meta-analyses [10]. This approach will enable a rigorous synthesis of available information, facilitating a better understanding of the methodologies applied in clinical practice and contributing to the development of evidence-based therapeutic strategies.

This study aims to analyze the methodology used in research on the treatment of PIPJ stiffness to assess its homogeneity and detect inconsistencies that may affect the validity of evidence-based clinical recommendations. Through a systematic review, the study seeks to identify patterns in study design, intervention selection criteria, and the quality of reported data, with the goal of providing a more structured foundation for future research and improving decision-making in clinical practice.

2. Materials and Methods

2.1. Inclusion and Exclusion Criteria

To ensure the replicability of the study, strict inclusion and exclusion criteria were established. Studies addressing PIPJ stiffness, regardless of the underlying etiology, were included. Various methodological approaches were considered, including randomized controlled trials (RCTs), quasi-experimental studies, observational and retrospective studies, systematic reviews, case studies, and expert opinions. To guarantee the clinical applicability of the findings, studies in which PIPJ stiffness was not the primary condition were excluded. Furthermore, included studies were required to report outcome measures related to joint mobility and functionality, such as range of motion (ROM), DASH and QuickDASH scores, pain levels, and treatment-related complications. Studies that lacked clearly specified outcome measures were excluded to prevent bias in data interpretation. Initially, studies in English and Spanish were considered. However, publications in Spanish were excluded due to a lack of methodological rigor in the clinical guidelines and available literature on PIPJ. Priority was given to studies published in indexed journals and internationally recognized databases. The analysis included orthopedic treatments with customized orthoses, surgical interventions, and conservative strategies such as manual therapy and dynamic orthoses. The effectiveness of the treatments was not directly compared; rather, the validity and coherence of their methodological designs were assessed. The observed heterogeneity hindered comparisons between studies and highlighted the need for standardized criteria in future research. The broad inclusion criteria initially resulted in the identification of numerous studies. However, the application of strict methodological standards reduced the dataset to those of higher quality and comparability, reflecting the challenges of systematically reviewing an area with diverse clinical approaches.

2.2. Search Strategy and Study Selection

A systematic search was conducted in PubMed, Cochrane, PEDro, and ScienceDirect using MeSH terms and keywords combined with Boolean operators. The search terms used were

• “proximal interphalangeal joint stiffness”
• “elastic-tension orthoses”
• “hand rehabilitation”
• “joint range of motion”
• “orthopedic splinting”
• “dynamic orthoses”

Relevant references were incorporated into the search strategy to facilitate the identification of related studies and improve the replicability of the process (see Figure 1). The search period covered the inception of the databases up to January 2023. Recent studies by Punsola Izard were excluded to prevent bias in the interpretation of previous literature.

Study selection was conducted in two phases following PRISMA [10]:

• Two independent reviewers (VP and AC) screened titles and abstracts.
• Full texts of the preselected studies were reviewed to verify their methodological rigor and relevance.

Discrepancies were resolved by consensus or, if necessary, through consultation with a third reviewer (XM).

2.3. Data Extraction and Management

Data extraction was performed independently by two authors using a pretested form. Information was collected on study design, participant characteristics, treatments, and outcome measures such as ROM improvement, functionality, complications, and pain levels. Additionally, timelines for data extraction were established to ensure consistency and adherence to the study protocol. The systematic review started in July 2023 and continued until February 2024, following PRISMA guidelines to ensure methodological rigor.

2.4. Data Análisis

The data analysis combined quantitative and qualitative approaches, depending on the availability and quality of the extracted information. Various elements were compared across the included studies, such as author, year, study type, number of participants, intervention, outcome measures, key findings, and risk of bias. This comparison allowed for an evaluation of methodological consistency and the relevance of findings in different contexts.

For studies reporting numerical data on the range of motion (ROM) of the proximal interphalangeal joint (PIPJ), mean differences (MD) and weighted mean differences (WMD) were calculated with 95% confidence intervals (CIs) [11,12]. The certainty of the evidence was assessed using the GRADE system [13,14], considering methodological quality, consistency, and precision of results.

The risk of bias was evaluated using the Cochrane Risk of Bias tool (RoB 2) for randomized controlled trials (RCTs) and the ROBINS-I tool for non-randomized studies [15,16]. Several key domains were analyzed, including study design, blinding, attrition, and co-interventions, assigning each a risk level categorized as low (0), uncertain (1), or high (2). The assessment was conducted independently by two reviewers, resolving any discrepancies through consensus.

To ensure the accuracy and reproducibility of calculations, JAMOVI software 2.5 (The JAMOVI Project, 2024) was used. Additionally, Python (2024) and Matplotlib (2024) were employed for graphical data representation, bias detection, and the generation of a heatmap to visualize bias patterns across the included studies (see Figure 2). In this heatmap, each row represents an evaluated criterion, and each column represents a study, providing a clear overview of the extent of bias in the analyzed evidence.

This methodology structured the analysis rigorously, ensuring that conclusions were based on the best available evidence and emphasizing the importance of considering bias risk in result interpretation.

3. Results

3.1. Study Selection

Figure 1 illustrates the process of study inclusion in the present systematic review. Initially, a broad search strategy was employed, leading to the identification of a substantial number of records. Subsequently, strict refinement criteria, based on robust methodological standards, were applied, resulting in the selection of 32 studies that met the inclusion criteria and were incorporated into the final synthesis. Additionally, three studies published after the initial cutoff date of January 2023 were included due to their high relevance to the topic under investigation. Consequently, the total number of studies included amounted to 35.

Each of these studies evaluated key aspects that allowed for a comprehensive comparison of the methodologies employed. To this end, data such as study type, authors and year of publication, methods for assessing joint stiffness (via range of motion [ROM] or other techniques), sample characteristics, therapeutic interventions, outcome measures (including active and passive ROM, patient satisfaction, pain intensity, and complications), main findings, risk of bias (considering study design, blinding, management of participant loss, and control of co-interventions), and treatment duration were extracted and analyzed.

3.2. Typology of Included Studies

A total of 32 studies were included, classified into four main categories:

• Basic Research (n = 4; 12.5%): Studies focused on the anatomical and biomechanical analysis of the PIP joint without direct clinical intervention.
• Observational Clinical Studies (n = 6; 18.8%): Investigations describing real or retrospective clinical outcomes without a controlled intervention.
• Interventional Clinical Studies (n = 13; 40.6%): Studies actively evaluating and comparing different therapeutic approaches, including surgical, orthotic, and rehabilitative treatments.
• Reviews and Evidence Synthesis (n = 9; 28.1%): Studies centered on systematic literature reviews as well as the analysis of current concepts and treatments.

3.3. Assessment of Joint Stiffness

Various methods for assessing PIP joint stiffness were identified. These approaches ranged from anatomical dissections to functional evaluations of range of motion (ROM) in different clinical and experimental contexts. ROM emerged as the predominant method among the analyzed studies, including pre- and post-intervention measurements in patients undergoing arthroplasties, orthotic treatments, or therapeutic manipulations.

Several studies reported significant improvements in flexion (up to 25°) and extension (up to 34°) following prolonged rehabilitation protocols. In dynamic orthosis studies, an average improvement of 9.1° was observed over a four-week period.

Biomechanical studies explored PIP joint stability in cases of fractures and dislocations, determining that joint stability depended on the displacement threshold in dorsal dislocations, with critical values defining instability. Additionally, the use of dynamic external fixators allowed patients to achieve an average active ROM of 89° after six months of follow-up.

Regarding the comparison of orthotic devices, the effectiveness of custom-designed versus prefabricated models was assessed. It was concluded that custom-made orthoses significantly restricted joint movement, whereas prefabricated models offered greater flexibility. Furthermore, progressive mobilization orthoses were examined in patients with flexion contractures, demonstrating a ROM improvement of up to 40° in long-term follow-up.

The impact of PIP joint arthrodesis angles on hand function was also analyzed. It was observed that fusions at 40° and 20° did not result in significant differences in grip strength, whereas fusion at 0° negatively affected overall functionality.

In terms of precision and methodological limitations, anatomical studies provided detailed data on innervation and joint structure, though with limited clinical applicability. Conversely, ROM assessments were highly dependent on the protocol and follow-up duration. Methodological biases were identified in retrospective studies, while systematic reviews provided a comprehensive yet heterogeneous overview of the results.

In summary, methods for measuring joint stiffness exhibited variability in precision and applicability, with ROM being the most commonly used measure. However, its reliability was constrained by the heterogeneity of study protocols and populations.

3.4. Participant Characteristics

The included studies encompassed a diverse range of participants, classified according to the methodological design employed. In clinical studies, participants consisted of patients who had undergone PIP arthroplasties, with sample sizes ranging from 28 to 299 individuals. Additionally, patients with flexion and extension contractures, volar plate avulsion fractures, and chronic PIP dislocations were included, as well as individuals with specific conditions such as trigger finger and swan-neck deformity.

Parallelly, some experimental studies included healthy volunteers to assess joint biomechanics under controlled conditions. Other studies relied on biomechanical modeling without patient data, focusing on structural simulations.

Moreover, several anatomical studies utilized cadaveric samples to evaluate joint stiffness and PIP biomechanics, analyzing between 15 and 52 cadaveric fingers from different donors. Finally, systematic reviews synthesized information on joint contractures, post-traumatic complications, and therapeutic strategies, providing a comprehensive overview despite being subject to the methodological heterogeneity of the included studies.

3.5. Interventions and Outcome Measures

The studies analyzed encompassed a wide range of interventions and outcome measures aimed at assessing PIP joint stiffness. Among surgical procedures, total PIP arthroplasty with different types of implants, open reduction and stabilization of fractures, percutaneous A1 pulley release for the treatment of flexion contractures, and vascularized joint transfer from the foot for PIP joint reconstruction were identified. Complementary orthopedic and rehabilitation treatments included the use of extension and progressive mobilization orthoses, specific splints for correcting swan-neck deformity and trigger finger, and neuromuscular taping for pediatric PIP sprain recovery. Experimental interventions covered biomechanical and joint stability studies on fractures and dorsal dislocations, PIP arthrodesis simulations with thermoplastic splints at different angles, and dynamic external fixation for stabilizing unstable fractures. Additionally, systematic reviews and comparative analyses facilitated the evaluation of therapeutic strategies, contrasting conservative and surgical approaches while reviewing post-traumatic complications.

To assess intervention effectiveness, the studies employed a variety of outcome measures. The range of motion (ROM) was the primary metric used, enabling the evaluation of flexion and extension improvements before and after treatment, with particular attention to differences between active and passive ROM. Joint stability was also assessed through displacement thresholds in dorsal dislocations, while grip strength was measured at various PIP fusion angles. Pain reduction and patient satisfaction were relevant parameters, considering post-treatment pain relief and satisfaction levels after surgical and orthotic interventions in relation to residual mobility. Furthermore, postoperative complications and secondary outcomes were analyzed, including complication rates, persistent joint stiffness, and the need for reintervention in cases where conservative treatment was unsuccessful. Overall, the reviewed studies implemented a variety of therapeutic approaches and evaluation methodologies, with clinical trials and biomechanical studies providing the most precise measurements. However, while systematic reviews offered a comprehensive perspective, their interpretation was constrained by the methodological heterogeneity of the included studies.

3.6. Key Findings

The reviewed studies provided significant findings regarding PIP joint biomechanics, the effectiveness of different therapeutic strategies, and the factors influencing rehabilitation. From an anatomical perspective, it was determined that the PIP joint is primarily innervated by palmar digital branches, while dorsal branches were only identified in the little finger. In cases of fractures and dorsal dislocations, instability significantly increased when more than 50% of the joint surface was compromised. Regarding interventions, dynamic splints demonstrated greater efficacy in improving active PIP extension compared to static splints, whereas custom-made splints restricted flexion more than prefabricated models. The Edinburgh immobilization position showed variable effects on joint stiffness, while PIP blocking splints proved more effective than MCP blocking splints in reducing pain and improving function.

When comparing surgical and conservative treatments, non-surgical therapy was generally preferred, with surgery reserved for cases where conservative treatment had failed. Surgical outcomes for PIP contractures were not encouraging, emphasizing the importance of early rehabilitation and the use of orthoses to prevent joint stiffness. For swan-neck deformities, splints were effective in mild cases, while severe deformities required surgical intervention. In the context of fractures and dislocations, dynamic external fixation improved both ROM and joint stability, achieving a mean post-treatment ROM of 89°. Regarding PIP arthroplasty, silicone implants were the preferred option due to their lower revision rates, although post-traumatic arthritis increased the risk of reintervention. Higher revision rates were identified in patients under 60 years old (25%), while PIP fusion at angles between 20° and 40° resulted in better functionality compared to fusion at 0°, which significantly impaired grip strength.

In summary, the findings highlight the importance of selecting the most appropriate treatment based on the severity of the pathology, prioritizing dynamic orthoses and conservative strategies in most cases. However, the methodological variability among the reviewed studies limits the possibility of establishing a definitive consensus on the optimal approach for each specific clinical condition.

3.7. Risk of Bias

The analysis of the risk of bias in the included studies reveals significant heterogeneity in methodological quality, with a variable distribution across different evaluated domains. As illustrated in Figure 2, biases were identified in several key categories, including study design, blinding, loss to follow-up, and co-interventions.

Regarding study design, a substantial proportion of studies exhibited a high risk of bias, as reflected in the predominance of scores of 2. This suggests methodological shortcomings, particularly due to the absence of randomized designs or adequate controls. However, a subset of studies achieved low-risk scores, indicating an appropriate methodological level in certain cases.

Blinding was another domain with notable deficiencies, with a considerable proportion of studies presenting high risk scores. This limitation is particularly relevant in clinical studies, where assessment bias may influence the interpretation of results. The lack of adequate blinding can lead to an overestimation of intervention effects, thereby compromising the validity of the findings.

Loss to follow-up emerged as a critical risk factor in several studies, with a heterogeneous distribution of scores. While some studies demonstrated adequate management of missing data, others exhibited a high risk of bias due to elevated dropout rates without appropriate imputation strategies.

Finally, in the category of co-interventions, a high proportion of studies received high risk scores. This factor may impact result interpretation by introducing uncontrolled variability in the application of interventions. The presence of undeclared or poorly documented co-interventions represents a significant limitation for the comparability of the included studies.

Overall, the identified risk of bias in the included studies limits the robustness of the synthesized evidence. The high methodological heterogeneity underscores the need for future studies with more rigorous designs, incorporating adequate blinding strategies, strict control of follow-up losses, and greater transparency in co-intervention documentation. These aspects will be fundamental in improving the internal and external validity of research in this field.

4. Discussion

PIPJ stiffness has been recognized as a significant clinical challenge since its first mention in the 1950s. This condition affects multiple anatomical structures, including the joint capsule, tendons, ligaments, and soft tissues, all contributing to restricted ROM [44,45]. However, despite advancements in the conceptual understanding of this pathology, there is an ongoing debate regarding the role of the placebo effect in joint recovery. Some studies suggest that ROM improvement may occur without the need for specific therapeutic interventions, raising doubts about the actual effectiveness of the treatments employed and the quality of the supporting evidence.

Given this uncertainty, it is crucial to examine how scientific evidence has been utilized in PIPJ treatment, specifically by analyzing the methodological quality of published studies. The primary objective of this study was to compare the methodologies of different investigations to determine whether the reported ROM improvements are supported by a rigorous and reliable methodological design. Without a solid methodology, it is impossible to establish with certainty whether a treatment is truly effective or whether the observed outcomes result from external factors such as the natural progression of the condition or a placebo effect.

Unfortunately, this systematic review demonstrates that almost all evaluated studies exhibit significant methodological inconsistencies, compromising the validity of their conclusions. Deficiencies in study design persist, including inadequate follow-up, lack of blinding, absence of control groups, small sample sizes, and failure to account for co-interventions. These limitations hinder the establishment of a treatment based on solid scientific evidence, as any intervention applied without a strong methodological framework cannot be considered true science.

This review included 32 studies, of which only six provided sufficient quantitative data to calculate the weighted mean difference (WMD) in PIPJ ROM: [18,19,36,38,46,47]. These studies reported a WMD of 28.98° (95% CI: 26.86–31.10°), which, in principle, would indicate a significant improvement in ROM. However, the diversity of evaluated interventions—including surgical procedures, PIPJ manipulation, orthotic devices, and conservative approaches—makes it impossible to isolate the specific impact of each treatment. Moreover, the absence of key data, such as baseline, intermediate, and final ROM values along with standard deviations, and the failure to control for co-interventions seriously compromise the reliability of these findings.

Quantitative data extracted from recent studies provide additional insights into documented improvements in PIPJ treatments. Wagner [18] reported that patients under 60 years of age had a revision rate of 25%, suggesting potential long-term stability improvement after arthroplasty. Tan et al. [19] found that dorsal dislocations became unstable when displacement exceeded 50%, supporting the importance of surgical or conservative stabilization strategies. Arauz et al. [48] demonstrated that PIPJ fusion at an angle of 20–40° resulted in superior function compared to fusion at 0°. Xu et al. [21] observed that grip strength differences between fusions at 40° and 20° were minimal, suggesting that the choice of fusion angle may have a limited impact on hand functionality. Costa [49] indicated that orthoses could maintain an extension force between 100 and 300 g, potentially contributing to stiffness reduction and ROM improvement.

However, despite the presence of these numerical data, a crucial limitation persists: Many studies do not specify how these values were obtained, the exact therapeutic moment at which the data were recorded, or whether standard deviation ranges were reported. The lack of these essential details makes it impossible to accurately compare results across studies without introducing significant methodological errors. Without uniformity in data collection and reporting, any comparison between different interventions remains speculative rather than conclusive.

To address these methodological deficiencies, the authors of this review have developed studies proposing more controlled experimental models, with the goal of initiating a new phase in scientific literature on PIPJ. The first study explored the influence of total end-range time (TERT) on PIPJ recovery, identifying that this factor may play a key role in ROM improvement. Instead of merely analyzing the effectiveness of a specific treatment, this study established a standardized framework for measuring ROM progression within clinical research [50]. The second study focused on the dose–response relationship between TERT and ROM improvement, proposing a quantifiable model for assessing therapeutic progression. This approach seeks to eliminate ambiguities in the existing literature and facilitate more homogeneous comparisons between future studies [50]. The third study, from a biomechanical perspective, analyzed differences between elastic-tension orthoses and conventional devices, evaluating parameters such as pressure distribution and the risk of skin injuries. Through a more structured methodology, objective criteria were established to compare different therapeutic approaches in future research [51]. The fourth study proposed an adaptive protocol based on the patient’s ROM progression, allowing for gradual treatment adjustments. This dynamic model has the potential to serve as a reference for future research, ensuring that interventions are evaluated with reproducible and well-defined criteria [52]. Building upon these prior findings, Punsola-Izard et al. [53] conducted a cadaveric study aimed at refining the understanding of PIPJ biomechanics and its implications for therapeutic strategies. Their research demonstrated that the mid-flexion position (30–40°) maximizes capsular space volume, facilitating ligament shortening and arthrofibrosis, which reinforces the need to prioritize proximal interphalangeal joint (PIPJ) extension in clinical settings. Through high-pressure silicone and latex injections, they identified that joint position plays a crucial role in capsular space distribution and mobility restriction, supporting previous findings on TERT and ROM improvement. Their results emphasize that immobilizing the PIPJ in extension with dorsal compression may be the most beneficial strategy to prevent contractures and arthrofibrosis, aligning with previous recommendations on structured rehabilitation protocols. Furthermore, their study provides a strong anatomical and biomechanical foundation to justify the application of manual therapy in mid-flexion to maximize joint accessory movements while minimizing friction. By integrating these findings with previous controlled experimental models, this research contributes to a more standardized and evidence-based approach to PIPJ rehabilitation, offering clinicians a clearer framework for intervention and supporting the development of adaptive, patient-specific treatment protocols.

4.1. Implications for Clinical Practice and Health Policy

The treatment of PIPJ stiffness remains a significant challenge in hand rehabilitation, and for clinical studies in this area to be useful and replicable, it is crucial that clinicians collect data systematically and in a standardized manner. First, the research objectives must be clearly defined, with specific research questions and well-established null and alternative hypotheses. The research question should focus on a key aspect of PIPJ treatment, such as the effectiveness of a specific intervention, and be formulated in a way that allows for a precise evaluation of the intervention under study. Clinicians must measure the ROM of the joint in a standardized way, using validated measurement tools such as digital goniometers or 2D or 3D analysis systems, ensuring that the same techniques are consistently used for each patient. Furthermore, it is necessary to record the standard deviation of measurements to accurately assess the variability of the data.

The treatment should follow standardized protocols that clinicians can replicate consistently. This includes specifying the type of intervention (e.g., orthoses, PIPJ manipulation, etc.), its frequency, duration, and intensity, and ensuring that the same criteria apply to all patients. The intervention must be clearly documented to guarantee that it can be replicated in future studies or other clinical settings. Additionally, it is crucial to limit co-interventions or carefully record any other treatments the patients may be receiving to avoid interference with the results. It is essential that studies not only focus on clinical data but also include patient-centered outcomes, such as QoL, pain reduction, and functional improvements. These data provide a comprehensive picture of how treatment impacts the daily lives of patients. To achieve this, clinicians should use standardized questionnaires that measure these outcomes, such as DASH or QuickDASH, which capture the patient’s subjective experience regarding their function and well-being.

Long-term follow-up is essential to assess whether the effects of treatment are sustainable. Clinicians should perform ROM measurements and other outcomes at regular intervals, such as 1, 3, 6, and 12 months, to assess the patient’s progress and whether PIPJ stiffness recurs after treatment. It is important that all measurements are taken under similar conditions to ensure the reliability and consistency of the data. Additionally, clinicians must record all aspects of the patient’s progress in detail. This includes not only ROM measurements but also the patient’s progress in terms of functionality, pain level, and any changes in treatment or symptoms. This information provides context and helps interpret the results more accurately.

One of the major issues identified in previous studies is the lack of standardized protocols to prevent the recurrence of stiffness after treatment. Clinicians should implement clear and documented preventive strategies that include recommendations for the use of orthoses, exercise, and other interventions to reduce the risk of stiffness reoccurrence. Since each patient may respond differently to interventions, it is important for clinicians to follow a personalized approach. Protocols should allow for adaptations based on the patient’s response to treatment. This includes adjustments to the intensity or duration of interventions depending on the ROM evolution and the patient’s tolerance. Clinicians should document these changes and make dynamic adjustments to the treatment plan as needed.

It is essential that clinicians and researchers work closely in data collection, ensuring that all values and measurements are reported consistently and in detail. This includes ensuring that the data are accessible for subsequent analysis, which will facilitate the interpretation of the results. For studies to be useful and replicable, it must be ensured that data collection procedures and techniques are transparent and reproducible in future research or other clinical settings.

4.2. Limitations of the Review

This review adhered to the PRISMA 2020 guidelines but was limited by the significant heterogeneity among the included studies and the lack of standardization in data collection. It is important to note that these limitations are not attributable to the researchers of this study but to the deficiencies in the existing scientific literature on the treatment of PIPJ stiffness. The inability to conduct a robust quantitative meta-analysis, including the use of the I² statistic, was due to the lack of detailed information, such as SD for changes in ROM, reflecting inconsistencies in the reporting methods across the studies analyzed. The inclusion of studies with diverse methodologies and varying sample sizes also limited the applicability of the findings to clinical practice, highlighting the need for stricter inclusion criteria and more methodological rigor in future research. The studies included in this review showed considerable heterogeneity in terms of the therapeutic approaches applied, the methodology used, and the characteristics of the patient populations. This variability, inherent in the existing studies, complicated the synthesis of results and reduced the ability to conduct robust statistical analyses. The lack of adequate control over co-interventions and the absence of complete quantitative data, such as baseline, intermediate, and final ROM values along with their standard deviations, reflected the methodological limitations in the literature, undermining the reliability of the findings and complicating the comparison between studies. Furthermore, inconsistencies in follow-up criteria and outcome measures, such as quality of life or patient satisfaction, made it difficult to comprehensively assess the treatment effects.

5. Conclusions and Future Perspectives

The findings of this systematic review indicate that, although multiple studies report improvements in the ROM of the PIPJ following various therapeutic interventions, the lack of methodological rigor in most of these studies prevents drawing solid conclusions regarding the actual effectiveness of the treatments. The vast majority of the analyzed studies present significant methodological limitations, including the absence of standardized protocols, inadequate controls, data collection biases, small sample sizes, and insufficient follow-up. Additionally, the lack of essential data, such as baseline, intermediate, and final ROM values, along with their standard deviations, as well as the absence of control over co-interventions, hinders study comparisons and raises doubts about the validity of their conclusions.

This review highlights the urgent need to improve methodological quality in research on PIPJ treatment. The issue is not merely developing new interventions but ensuring that future studies follow rigorous, transparent, and replicable protocols, allowing for the generation of knowledge that is truly evidence-based. To achieve this, it is essential that future research implements methodologically robust designs, with well-defined inclusion and exclusion criteria, standardized outcome measures, and adequate controls to ensure the validity of the findings. It is also crucial to standardize data collection by using validated measurement tools and ensuring precise reporting of clinical results, including ROM values and their progression, to enable reliable comparisons between studies. Furthermore, efforts must be made to eliminate biases in result interpretation, ensuring that reported improvements are contextualized within a robust methodological design that accounts for external factors or potential placebo effects.

Another key priority is the development of long-term follow-up protocols to assess the sustainability of interventions and prevent the recurrence of stiffness after treatment. Additionally, it is critical to integrate patient-centered outcomes, such as QoL and treatment satisfaction, to evaluate the real impact of interventions on patients’ daily lives.

In conclusion, this review has demonstrated that the existing literature lacks adequate methodologies to rigorously assess the effectiveness of PIPJ treatments. Until these deficiencies are addressed, any intervention applied without a solid methodological framework cannot be considered evidence-based science but rather an unsupported practice. To advance the treatment of PIPJ stiffness, future research must adopt stricter methodological criteria, standardized protocols, and a rigorous approach, ensuring the development of reliable scientific knowledge applicable to clinical practice.