Biomechanics of the knee extensor mechanism and its relationship to patella tendinopathy: A review

Morphological characteristics of the patellar tendon in runners, cyclists, triathletes, and physically active individuals

The objective of the study was to compare measurements of length, thickness, and cross-section area (CSA) of the patellar tendon (PT) among cyclists, runners, triathletes, and physically active individuals (control group). Forty healthy individuals (10 cyclists, 10 runners, 10 triathletes, and 10 physically active individuals) aged between 18 and 45 years (30.3 ± 8.6 years) participated in the study. PT was measured by a B-mode ultrasound system. To measure the length and thickness (in 5, 10, 15, and 20 mm of the PT length) the probe was positioned parallel to the tendon and to measure the CSA the probe was positioned perpendicularly in 25, 50, and 75% of the PT length. PT length data were analyzed using a one-way ANOVA to compare between groups and PT CSA and thickness were analyzed using a two-way ANOVA (group vs. position) to compare the variables among the groups with the post-hoc Tukey test. All statistical analyses were performed considering p < 0.05. We observed a significant difference, where cyclists had smaller PT thickness (regardless of the location measured) compared to the group of triathletes (p = 0.001) and the physically active group (p = 0.043). All other variables (length, thickness, and CSA) and interactions (local and position) were not significant. We concluded that regardless of the position where PT thickness is measured, cyclists have smaller PT thickness compared to triathletes and physically active individuals but similar when compared to runners. And no differences in the length and CSA of the PT between groups.

Patellofemoral Disorders in Soccer Players

Patellofemoral disorders are common in the world of soccer and impact players across all levels and ages of the sport. Patellofemoral disorders encompass a spectrum of conditions, from anterior knee pain to patellar instability, and are often influenced by complex biomechanical factors and anatomic variations that can predispose to these conditions. In recent years, there has been a growing emphasis on injury prevention strategies and data-driven approaches, championed by organizations like the Union of European Football Associations and individual professional clubs. Conservative management remains the initial approach for many players, including physical therapy and supportive devices. However, surgical intervention, particularly in cases of recurrent patellar dislocations, is often necessary. The understanding of patellofemoral biomechanics in soccer continues to evolve and offers opportunities for more effective injury prevention and tailored treatment strategies. Despite the challenges, a comprehensive approach to patellofemoral disorders in soccer is essential to preserve player health, enhance performance, and sustain the sport's vitality.

Universal optimal design in the vertebrate limb pattern and lessons for bioinspired design

This paper broadly summarizes the variation of design features found in vertebrate limbs and analyses the resultant versatility and multifunctionality in order to make recommendations for bioinspired robotics. The vertebrate limb pattern (e.g. shoulder, elbow, wrist and digits) has been proven to be very successful in many different applications in the animal kingdom. However, the actual level of optimality of the limb for each animal application is not clear because for some cases (e.g. whale flippers and bird wings), the basic skeletal layout is assumed to be highly constrained by evolutionary ancestry. This paper addresses this important and fundamental question of optimality by analysing six limbs with contrasting functions: human arm, whale flipper, bird wing, human leg, feline hindlimb and frog hindlimb. A central finding of this study is that the vertebrate limb pattern is highly versatile and optimal not just for arms and legs but also for flippers and wings. One key design feature of the vertebrate limb pattern is that of networks of segmented bones that enable smooth morphing of shapes as well as multifunctioning structures. Another key design feature is that of linkage mechanisms that fine-tune motions and mechanical advantage. A total of 52 biomechanical design features of the vertebrate limb are identified and tabulated for these applications. These tables can be a helpful reference for designers of bioinspired robotic and prosthetic limbs. The vertebrate limb has significant potential for the bioinspired design of robotic and prosthetic limbs, especially because of progress in the development of soft actuators.

Patellar Resurfacing Is Not a Risk Factor for Postoperative Patella Baja in Total Knee Arthroplasty

Background

Patella baja is a known complication of total knee arthroplasty (TKA). There is a limited understanding of the association between patellar resurfacing and the incidence of patella baja. We aimed to compare rates of patella baja between unresurfaced and resurfaced patellas in patients undergoing TKA.

Methods

A retrospective review of patients who underwent TKA between October 2009 and January 2020 was performed. Patients were included if they had at least one preoperative radiograph and a 1-year follow-up radiograph. Blackburne-Peel index (BPI) and Insall-Salvati ratios (ISRs) were measured on preoperative and 1-year postoperative radiographs and were used to define patella baja vs pseudopatella baja. Statistical analysis was performed using a linear model analysis of variance and the Fisher's exact test.

Results

Three hundred eighteen TKAs were included, with 176 being resurfaced and 142 unresurfaced patellas. Of the resurfaced group, 4% (7/176) had true patella baja, compared to 5.6% (8/142) of the unresurfaced patellas. Of the resurfaced patellas, 8% (14/176) had pseudopatella baja, compared to 7% (10/142) in the unresurfaced group. Patellar resurfacing was not associated with a higher incidence of patella baja (P = .60) or pseudopatella baja (P = .83). Lower preoperative ISRs (P = .04) and BPIs (0.03) were highly predictive of a higher incidence of patella baja post-TKA.

Conclusions

Patellar resurfacing in TKA is not associated with a higher incidence of patella baja in TKA when compared to unresurfaced patellas. Lower preoperative ISRs and BPIs are highly predictive of a higher incidence of postoperative patella baja.

Knee Extensor Apparatus Reconstruction with Allograft after Patellar Resection: A Case Report

Background

The extensor apparatus of the knee can be thought of a chain that transmits the muscular strength developed by the quadriceps muscles to the proximal tibia. This complex is essential to allow the extension of the tibia over the femur, being essential to provide knee mobility and stability. In case of lesions which irreparably damage the patella, such as a locally aggressive bone tumor, it is necessary to restore both the apparatus' anatomical continuity and its strength.

Case report

A 39-years-old Caucasian man with a history of lung carcinoma developed atraumatic swelling and soreness in his left knee. Imaging evidence reported a degeneration of the left patella. We performed an en bloc resection of the patella and the nearby soft tissues of the extensor apparatus. The resulting gap was fulfilled with a massive allograft consisting of a quadriceps tendon, a patella and a patellar ligament. No complication or local recurrences were observed. At the patient's latest follow-up, he did not have any extension lag and quadriceps strength was completely restored.

Conclusion

Massive allografts can represent a reliable alternative for the reconstruction of the patella and the knee extensor apparatus in orthopedic oncology.

Surgical treatment of chronic proximal patellar tendon tears grades 3 and 4 using augmentation with quadriceps tendon-bone graft

BACKGROUND

Chronic proximal patellar tendinosis with partial tendon tears represents a multifactorial overuse injury. Several surgical techniques have been described with various outcomes and the return to sports may fail.

HYPOTHESIS

Reconstruction of the proximal patellar tendon with augmentation using a quadriceps tendon-bone (QTB) graft improves knee function in patients presenting with proximal patellar tendinosis and partial tendon tears.

METHODS

Forty-seven patients (32 males, 15 females) with chronic proximal patellar tendinosis and tendon tears grade 3 and 4 were treated between 1992 and 2018. Patients were evaluated retrospectively using the Popkin-Golman (PG) MRI grading system and the removed tendon parts. The Tegner Activity Scale (TAS) and the Numerical Rating Scale (NRS) for pain were used as outcome measures before surgery and at follow up. Complete data were available in 100% of cases at 6 months follow up, and fifteen of them at later follow up.

RESULTS

The average follow up was 1.5 years (range, 0.5-16). The TAS improved from a mean preoperative score of 3.7 to a mean postoperative score of 9.1. The median NRS status decreased from an average of 6.4 to 1.1. Two patients needed additional arthroscopic scar tissue removal.

CONCLUSION

Reconstruction of proximal patellar tendon tears grades 3 and 4 with augmentation using a QTB graft is a valuable surgical salvage procedure in chronic cases. It improves knee function and yields good to excellent results in most cases including high level athletes. The use of MRI with the PG classification of tendon tears is highly recommended.

LEVEL OF EVIDENCE

Therapeutic case series, Level IV.

Bibliometric Analysis of the Top 50 Most Influential Studies on Patellar Tendon Injury

Background

There is a wide range of literature on patellar tendon injury, making it increasingly difficult to stay informed on the most influential studies in this field. It is essential to be familiar with the foundational articles of patellar tendon injury research to understand the current state of the literature and deliver high quality care.

Purpose

To objectively identify the 50 most influential articles relating to patellar tendon injury and conduct a bibliometric analysis to identify key features of these articles.

Study Design

Cross-sectional study.

Methods

The Clarivate Analytics Web of Knowledge database was utilized to gather metrics on the 50 most cited articles on patellar tendon injury on June 27, 2022. The information extracted from each article included publication year, number of citations, author information, article type, level of evidence, country of origin, journal name, study focus, and industry influence.

Results

The top 50 studies were cited a total of 8543 times and published between 1977 and 2015. The majority of articles were published after 2003, and the majority of citations were accrued after 2011. The most prevalent article types were cohort studies (n = 23), and the majority of studies were of evidence level 2 (n = 14) or 4 (n = 13). Australia and the United States (US) each published the most studies (n = 11). Only 4 (8%) studies focused on patellar tendon rupture, and 12 (24%) of the top 50 studies were associated with industry.

Conclusion

The majority of the top 50 most influential articles in patellar tendon injury were published and accumulated citations in the past 10 to 20 years. Non-US countries, institutions, and journals published many of the top 50 studies, reflecting a global interest and commitment to research in this field. Patellar tendon rupture and surgical repair represents a minority of research in the top 50 studies and could be a point of growth in the future.

MRI Characteristics and Alterations in Patellar Height in Patients with Patellar Tendinopathy-A Retrospective Study

(1) Background: Patellar tendinopathy (PT) is an overuse condition of the knee extensor mechanism characterized by ventral knee pain at the lower pole of the patella and limited functionality. (2) Methods: In this retrospective study, a group of patients with PT (n = 41) was compared with a control group (n = 50) in terms of patient-related data and magnetic resonance imaging (MRI) characteristics. (3) Results: Patellar height was higher in the PT patient group and there was a significant difference in Caton-Deschamps index (CD) compared to the control group (p = 0.021). Patients with PT showed a lower patella-patellar tendon angle (PPTA) (p = 0.011). The patellar tendon thickness (PTT) in the proximal (PTTprox), middle (PTTmid) and distal (PTTdistal) part of the tendon was significantly thickened (p < 0.001). Increased signal intensity in MRI was detected in symptomatic tendons over 6 months compared to a duration of less than 6 months (p = 0.025). A significant relationship between the PTTprox and an increased signal intensity was observed (p < 0.001). (4) Conclusions: Patients with PT showed a significant difference in the patellar height and PPTA. With persistence of symptoms over 6 months, MRI seems suitable to detect the morphologic tendon changes and further identify patients suitable for surgical procedures.

Achilles Tendon, Patellar Tendon, and Femoral Cartilage Thickness in Control vs Asymptomatic Flatfoot Young Adults

BACKGROUND

Changes in lower extremity alignment in individuals with flatfoot may be associated with differences in morphology of the tendons or cartilage in lower extremities. The purpose of the present study was to investigate the potential association of flatfoot with the morphology of the Achilles tendon, patellar tendon, and femoral cartilage.

METHODS

This study was conducted with 40 participants with flatfoot (28 females, 12 males) and 40 participants with a normal foot posture (28 females, 12 males). The thickness of the Achilles tendon (at points 2 and 3 cm proximal to the superior aspect of the calcaneus), patellar tendon (at the inferior pole of the patella and 1 cm proximal of the inferior pole of the patella), and femoral cartilage (at the intercondylar area, medial condyle, and lateral condyle) was measured by an ultrasonography device.

RESULTS

The Achilles tendon thickness at 2 cm (P = .009) and 3 cm (P = .010) proximal of the superior aspect of the calcaneus was on average 4% to 6% lower in individuals with flatfoot compared with controls. The cartilage thickness at the intercondylar area (P = .005) and medial condyle (P = .018) was on average 8% to 12% greater in individuals with flatfoot; however, the cartilage thickness at the lateral condyle and patellar tendon thickness was similar in both groups.

CONCLUSION

The results obtained suggest that foot posture is associated with the morphology of the Achilles tendon and femoral cartilage.

LEVEL OF EVIDENCE

Level III, diagnostic comparative study.

Changes in stiffness of the specific regions of knee extensor mechanism after static stretching

Decreased muscle stiffness could reduce musculotendinous injury risk in sports and rehabilitation settings. Static stretching (SS) has been used to increase the flexibility of muscles and reduce muscle stiffness, but the effects of SS on the stiffness of specific regions of the knee extensor mechanism are unclear. The quadriceps femoris and patellar tendon are essential components of the knee extensor mechanism and play an important role in knee motion. Therefore, we explored the acute and prolonged effects of SS on the stiffness of the quadriceps femoris and patellar tendon and knee flexion range of motion (ROM). Thirty healthy male subjects participated in the study. Three 60-s SS with 30-s intervals were conducted in right knee flexion with 30° hip extension. We measured the ROM and stiffness of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) and the proximal-(PPT), middle-(MPT), and distal-(DPT) region stiffness of the patellar tendon before and immediately after SS intervention, or 5 and 10 min after SS. The stiffness of the quadriceps muscle and patellar tendon were measured using MyotonPRO, and the knee flexion ROM was evaluated using a medical goniometer. Our outcomes showed that the ROM was increased after SS intervention in all-time conditions (p < 0.01). Additionally, the results showed that the stiffness of RF (p < 0.01) and PPT (p = 0.03) were decreased immediately after SS intervention. These results suggested that SS intervention could be useful to increase knee flexion ROM and temporarily reduce the stiffness of specific regions of the knee extensor mechanism.

Knee Extensor Mechanism Tendinopathy: Evaluation, Treatment, and Prevention

ABSTRACT

Knee extensor mechanism tendinopathy, including patellar and quadriceps tendinopathy, is common among athletes and those involved in jumping sports. It is largely a clinical diagnosis that presents as anterior knee pain and stiffness with associated tenderness over the affected tendon. Imaging modalities, including ultrasound and/or magnetic resonance imaging, may be helpful with the diagnosis of difficult cases or in the planning of interventional procedures. Focused and structured rehabilitation using eccentric or heavy slow resistance exercise in conjunction with load management is important for recovery. Adjuvant therapies (e.g., injections or surgery) may be necessary in recalcitrant cases or those with insufficient response to rehabilitation efforts. Prevention strategies focus on improving biomechanics, landing mechanism and lower-extremity balance, flexibility, and strength.

The Role of the Non-Collagenous Extracellular Matrix in Tendon and Ligament Mechanical Behavior: A Review

Tendon is a connective tissue that transmits loads from muscle to bone, while ligament is a similar tissue that stabilizes joint articulation by connecting bone to bone. The 70-90% of tendon and ligament's extracellular matrix (ECM) is composed of a hierarchical collagen structure that provides resistance to deformation primarily in the fiber direction, and the remaining fraction consists of a variety of non-collagenous proteins, proteoglycans, and glycosaminoglycans (GAGs) whose mechanical roles are not well characterized. ECM constituents such as elastin, the proteoglycans decorin, biglycan, lumican, fibromodulin, lubricin, and aggrecan and their associated GAGs, and cartilage oligomeric matrix protein (COMP) have been suggested to contribute to tendon and ligament's characteristic quasi-static and viscoelastic mechanical behavior in tension, shear, and compression. The purpose of this review is to summarize existing literature regarding the contribution of the non-collagenous ECM to tendon and ligament mechanics, and to highlight key gaps in knowledge that future studies may address. Using insights from theoretical mechanics and biology, we discuss the role of the non-collagenous ECM in quasi-static and viscoelastic tensile, compressive, and shear behavior in the fiber direction and orthogonal to the fiber direction. We also address the efficacy of tools that are commonly used to assess these relationships, including enzymatic degradation, mouse knockout models, and computational models. Further work in this field will foster a better understanding of tendon and ligament damage and healing as well as inform strategies for tissue repair and regeneration.

Current understanding of the diagnosis and management of the tendinopathy: An update from the lab to the clinical practice

Tendinopathy is labeled by many authors as a troublesome, common pathology, present in up to 30% medical care consultations involving musculoskeletal conditions. Despite the lasting interest for addressing tendon pathology, current researchers agree that even the exact definition of the term tendinopathy is unclear. Tendinopathy is currently diagnosed as a clinical hypothesis based on the patient symptoms and physical context. One of the main goals of current clinical management is to personalize treatment approaches to adapt them to the many different needs of the population. Tendons are complex structures that unite muscles and bones with two main objectives: to transmit forces and storage and release energy. Regarding the tensile properties of the tendons, several authors argued that tendons have higher tensile strength compared with muscles, however, are considered less flexible. Tendinopathy is an accepted term which is used to indicated a variety of tissue conditions that appear in injured tendons and describes a non-rupture damage in the tendon or paratendon, which is intensified with mechanical loading Even when the pathoetiology of tendinopathy is unclear, there is a wide array of treatments available to treat and manage tendinopathy. Although tendinitis usually debuts with an inflammatory response, the majority of chronic tendinopathies do not present inflammation and so the choosing of treatment should vary depending on severity, compliance, pain and duration of symptoms. The purpose of this article is to review and provide an overview about the currently research of the tendon diagnosis, management and etiology.

Sesamoid bones also show functional adaptation in their microanatomy-The example of the patella in Perissodactyla

The patella is the largest sesamoid bone of the skeleton. It is strongly involved in the knee, improving output force and velocity of the knee extensors, and thus plays a major role in locomotion and limb stability. However, the relationships between its structure and functional constraints, that would enable a better understanding of limb bone functional adaptations, are poorly known. This contribution proposes a comparative analysis, both qualitative and quantitative, of the microanatomy of the whole patella in perissodactyls, which show a wide range of morphologies, masses, and locomotor abilities, in order to investigate how the microanatomy of the patella adapts to evolutionary constraints. The inner structure of the patella consists of a spongiosa surrounded by a compact cortex. Contrary to our expectations, there is no increase in compactness with bone size, and thus body size and weight, but only an increase in the tightness of the spongiosa. No particular thickening of the cortex associated with muscle insertions is noticed but a strong thickening is observed anteriorly at about mid-length, where the strong intermediate patellar ligament inserts. The trabeculae are mainly oriented perpendicularly to the posterior articular surface, which highlights that the main stress is anteroposteriorly directed, maintaining the patella against the femoral trochlea. Conversely, anteriorly, trabeculae are rather circumferentially oriented, following the insertion of the patellar ligament and, possibly also, of the quadriceps tendon. A strong variation is observed among perissodactyl families but also intraspecifically, which is in accordance with previous studies suggesting a higher variability in sesamoid bones. Clear trends are nevertheless observed between the three families. Equids have a much thinner cortex than ceratomorphs. Rhinos and equids, both characterized by a development of the medial border, show an increase in trabecular density laterally suggesting stronger stresses laterally. The inner structure in tapirs is more homogeneous despite the absence of medial development of the medial border with no "compensation" of the inner structure, which suggests different stresses on their knees associated with a different morphology of their patellofemoral joint.

The Sagittal Tibial Tubercle-Trochlear Groove Distance as a Measurement of Sagittal Imbalance in Patients with Symptomatic Patellofemoral Chondral Lesions

Objective. To measure the sagittal alignment of the tibial tubercle through the sagittal tibial tubercle-trochlear groove (sTTTG) distance in patients with and without patellar chondral lesions. Design. Patients treated with patellofemoral cartilage restoration or repair procedures were retrospectively reviewed (group 1; N = 17). A control group of patients (group 2; N = 20) undergoing partial meniscectomy with normal patellar cartilage was included. An asymptomatic patellar chondrosis group (group 3; N = 15) was identified as patients undergoing partial meniscectomy with patellar cartilage wear. The sTTTG was measured on the preoperative axial T₂ magnetic resonance imaging (MRI) sequence. The first point was the nadir of the anterior trochlear cartilage, and the second point was the anterior tibial tubercle. A line was drawn between these points, perpendicular to the posterior condylar axis. Comparisons were made between the 3 groups using analysis of variance testing with Bonferroni corrections. Significance was defined as P < 0.05. Results. The mean sTTTG was significantly more posterior in group 1 (5.9 ± 5.5 mm posterior to the trochlear groove) relative to group 2 (0.8 ± 5.3 mm posterior; P = 0.018). The mean value for group 3 (2.7 ± 5.3 mm posterior) fell between group 1 and 3 but was not significantly different from group 1 (P = 0.31) or group 2 (P = 0.89). There were no significant differences with regards to sulcus angle, Caton-Deschamps Index, TTTG, or knee flexion angle on the MRI scan. Conclusions. A more posteriorly positioned tibial tubercle was observed in patients with patellar cartilage lesions relative to those with intact patellar cartilage. Intermediate positioning was observed in patients with asymptomatic patellar chondral wear. Level of Evidence. Level 3 diagnostic study.

Enthesis strength, toughness and stiffness: an image-based model comparing tendon insertions with varying bony attachment geometries

Tendons of the body differ dramatically in their function, mechanics and range of motion, but all connect to bone via an enthesis. Effective force transfer at the enthesis enables joint stability and mobility, with strength and stiffness arising from a fibrous architecture. However, how enthesis toughness arises across tendons with diverse loading orientations remains unclear. To study this, we performed simultaneous imaging of the bone and tendon in entheses that represent the range of tendon-to-bone insertions and extended a mathematical model to account for variations in insertion and bone geometry. We tested the hypothesis that toughness, across a range of tendon entheses, could be explained by differences observed in interactions between fibre architecture and bone architecture. In the model, toughness arose from fibre reorientation, recruitment and rupture, mediated by interactions between fibres at the enthesis and the bony ridge abutting it. When applied to tendons sometimes characterized as either energy-storing or positional, the model predicted that entheses of the former prioritize toughness over strength, while those of the latter prioritize consistent stiffness across loading directions. Results provide insight into techniques for surgical repair of tendon-to-bone attachments, and more broadly into mechanisms for the attachment of highly dissimilar materials.

Patella Alta: When to Correct and Impact on Other Anatomic Risk Factors for Patellofemoral Instability

Patella alta is described as abnormally high-riding patella in relation to the femur, the trochlear groove, or the tibia with decreased bony stability. Patella alta represents an important predisposing factor for patellofemoral instability. Different measurement methods are used to define patella alta. Despite the clinical importance of patella alta, there is only limited consensus on cutoff values, indications for treatment, and ideal correction. In addition, the impact of patella alta on other risk factors for lateral patellar instability is significant. This must be considered when assessing clinical complaints and choosing the best individual treatment. Combined surgical interventions may be necessary.

Sagittal patellar flexion angle measurement determines greater incidence of patella alta in patellar tendinopathy patients

PURPOSE

The objective of this study was to compare patellar height and patella alta between a control cohort and patients with patellar tendinopathy by the sagittal patellar flexion angle (SPFA) measurement.

METHODS

Magnetic resonance imaging (MRI) scans of the knee were obtained from a sports imaging facility and screened to select patients with anterior knee pain. This symptomatic group was divided into two patient cohorts: those with and without MRI features of patellar tendinopathy. Lateral knee radiographs were reviewed and SPFA, knee flexion angle and Insall-Salvati ratio (IS) were measured from the radiographs by two independent reviewers.

RESULTS

A total of 99 patients consisting of 48 patellar tendinopathy patients and 51 control patients were included. There was a significantly higher mean patellar height (p = 0.002, d = 0.639) and a greater patella alta incidence in the patellar tendinopathy cohort (25.0%) compared to the controls (3.9%) (p = 0.022, d = 0.312). Insall-Salvati ratio measurements showed no difference in patella alta incidence between tendinopathy and control cohorts. There was excellent inter- and intra-observer reliability of SPFA measurements (ICC 0.99).

CONCLUSION

This is the first study to demonstrate a greater incidence of patella alta in patellar tendinopathy patients compared to controls. A greater patella alta incidence amongst patellar tendinopathy patients as defined by SPFA was found to be clinically relevant, as it suggests these patients may comprise the recalcitrant patient subgroup who do not improve with current surgical intervention and may therefore benefit from a biomechanical surgical solution.

LEVEL OF EVIDENCE

III.

Expanded adipose derived mesenchymal stromal cells are effective in treating chronic insertional patellar tendinopathy: clinical and MRI evaluations of a pilot study

Purpose

Effect of ultrasound guided injections of autologous ASCs in chronic recalcitrant patellar tendinopathy.

Methods

Fourteen patients (16 knees, 12/2 males/females) with chronic, recalcitrant (unsuccessfully treated with nonoperative treatments) insertional PT underwent clinical evaluation and magnetic resonance imaging (MRI) before intervention. Stromal vascular fraction cells (SVF) were expanded by in-vitro culture and characterized by flow cytometry. Players were injected with three bi-weekly injections of ASCs followed by physiotherapy. They underwent serial clinical evaluations during a 12-month period with repeated MRI at 6-month post-injection.

Results

Victorian Institute of sports assessment-patellar tendon questionnaire (VISA-P) scores improved from 43.8 ± 4.9 at baseline to 58.1 ± 7.1, 70.3 ± 7.9 and 78.7 ± 7.5 at 3, 6, and12months follow-up, respectively. (p = 0.0004 comparing each variable with the previous one). Mean Visual analogue pain in sports (VAS-sport) score during practice significantly decreased from 7.4 ± 0.5 at baseline to 5.2 ± 1.5 9 (p = 0.0005), 3.3 ± 1.1 (p = 0.0004) and 1.5 ± 0.7 (P = 0.0004) at 3, 6, and 12 months, respectively. Mean Tegner-scores for patients were 8.0 ± 0.8 before injury and 2.3 ± 0.9 before treatment, thereafter, improving to 4.8 ± 0.8 and 7.2 ± 0.7 at 6- and 12- months, respectively (p = 0.0001). MRI assessed tendon width’ did not change over the first 6 months post-intervention. Significant changes were observed for: tendon thickness (12.8 ± 1.1 to 10.9 ± 0.7, P = 0.0001); tear length (9.3 ± 1.3 to 2.3 ± 0.7, P = 0.0001), tear width (6.3 ± 0.8 to 3.4 ± 0.4, P = 0.0001), and tear thickness (4.6 ± 0.4 to 2.6 ± 0., P = 0.0001) at baseline and 6 months, respectively.

Conclusion

Patients with recalcitrant insertional PT showed significant clinical improvement and structural repair at the patellar insertional tendinopathy after injections of autologous ASCs. Results of this study are promising and open a new biological therapeutic modality to treat PT.

Epidemiology of Acute Extensor Mechanism Injuries in Collegiate-Level Athletes in the United States

BACKGROUND

Extensor mechanism injuries involving the quadriceps tendon, patella, or patellar tendon can be a devastating setback for athletes. Despite the potential severity and relative frequency with which these injuries occur, large-scale epidemiological data on collegiate-level athletes are lacking.

STUDY DESIGN

Descriptive epidemiology study.

LEVEL OF EVIDENCE

Level 4.

METHODS

Knee extensor mechanism injuries across 16 sports among National Collegiate Athletic Association (NCAA) men and women during the 2004-2005 to 2013-2014 academic years were analyzed using the NCAA Injury Surveillance Program (NCAA-ISP). Extensor mechanism injuries per 100,000 athlete-exposures (AEs), operative rate, annual injury and reinjury rates, in-season status (pre-/regular/postseason), and time lost were compiled and calculated.

RESULTS

A total of 11,778,265 AEs were identified and included in the study. Overall, 1,748 extensor mechanism injuries were identified, with an injury rate (IR) of 14.84 (per 100,000 AEs). N = 114 (6.5%) injuries were classified as severe injuries with a relatively higher median time loss (44 days) and operative risk (18.42%). Male athletes had higher risk of season-ending injuries in both all (3.20% vs 0.89%, P < 0.01) and severe (41.54% vs 16.33%, P < 0.01) extensor mechanism injuries. Similarly, contact injuries were more frequently season-ending injuries (4.44% vs 1.69%, P = 0.01). Women's soccer (IR = 2.59), women's field hockey (IR = 2.15), and women's cross country (IR = 2.14) were the sports with the highest rate of severe extensor mechanism injuries.

CONCLUSION

Extensor mechanism injuries in collegiate athletes represent a significant set of injuries both in terms of volume and potentially to their athletic careers. Male athletes and contact injuries appear to have a greater risk of severe injuries. Injuries defined as severe had a higher risk of operative intervention and greater amount of missed playing time.

CLINICAL RELEVANCE

Knowledge of the epidemiology of extensor mechanism injuries may help clinicians guide their athlete patients in sports-related injury prevention and management.

Distalising tibial tubercle osteotomy decreases patellar tendon force - A treatment rationale for recalcitrant patellar tendinopathy

BACKGROUND

Patellar tendinopathy is an overuse condition affecting athletes, often with a high morbidity if left untreated. High-level evidence fails to support the use of surgery. A tibial tubercle osteotomy (TTO) has been suggested as a surgical option to improve patient outcomes. Our aim was to explore whether a distalising TTO will alter the patellar tendon to quadriceps tendon force ratio and the sagittal patellar tilt.

METHODS

Six cadaver limbs were placed in a custom jig with a mechanical testing machine applying cyclical loads of 200-500 N to the quadriceps tendon. The knee was fixed at 0, 15, 30, 45, 60, 75 and 90° of flexion and a buckle transducer recorded the resultant patellar tendon force. Testing was performed with the native tibial tubercle position and with the tubercle distalised by 11 mm. Testing was also performed with the tubercle anteriorised by 10 mm at both of these tubercle positions, a total of four different testing positions.

RESULTS

There was a significant decrease in the patellar tendon to quadriceps tendon force ratio from 30-60° of knee flexion. There was a significant increase in the sagittal patellar tilt at 30° of knee flexion with distalisation.

CONCLUSION

This biomechanical study shows that the patellar tendon to quadriceps tendon force ratio can be altered with a distalising tibial tubercle osteotomy. A tibial tubercle osteotomy may be a biomechanical treatment option for recalcitrant patellar tendinopathy by decreasing the load through the patellar tendon, allowing the athlete to maintain higher training volumes and loads.

Rethinking Patellar Tendinopathy and Partial Patellar Tendon Tears: A Novel Classification System

BACKGROUND

Patellar tendinopathy is an overuse injury of the patellar tendon frequently affecting athletes involved in jumping sports. The tendinopathy may progress to partial patellar tendon tears (PPTTs). Current classifications of patellar tendinopathy are based on symptoms and do not provide satisfactory evidence-based treatment guidelines.

PURPOSE

To define the relationship between PPTT characteristics and treatment guidelines, as well as to develop a magnetic resonance imaging (MRI)-based classification system for partial patellar tendon injuries.

STUDY DESIGN

Cohort study (prognosis); Level of evidence, 2.

METHODS

MRI characteristics and clinical treatment outcomes were retrospectively reviewed for 85 patients with patellar tendinopathy, as well as 86 physically active control participants who underwent MRI of the knee for other conditions. A total of 56 patients had a PPTT and underwent further evaluation for tear size and location. The relationship between tear characteristics and clinical outcome was defined with use of statistical comparisons and univariate and logistic regression models.

RESULTS

Of the 85 patients, 56 had partial-thickness patellar tendon tears. Of these tears, 91% involved the posterior and posteromedial regions of the proximal tendon. On axial MRI views, patients with a partial tear had a mean tendon thickness of 10 mm, as compared with 6.2 mm for those without (P < .001). Eleven patients underwent surgery for their partial-thickness tear. All of these patients had a tear >50% of tendon thickness (median thickness of tear, 10.3 mm) on axial views. Logistic regression showed that tendon thickness >8.8 mm correlated with the presence of a partial tear, while tendon thickness >11.45 mm and tear thickness >55.7% predicted surgical management.

CONCLUSION

Partial-thickness tears are located posterior or posteromedially in the proximal patellar tendon. The most sensitive predictor for detecting the presence of a partial tear was patellar tendon thickness, in which thickness >8.8 mm was strongly correlated with a tear of the tendon. Tracking thickness changes on axial MRI may predict the effectiveness of nonoperative therapy: athletes with patellar tendon thickness >11.5 mm and/or >50% tear thickness on axial MRI were less likely to improve with nonoperative treatment. A novel proposed classification system for partial tears, the Popkin-Golman classification, can be used to guide treatment decisions for these patients.

Treatment of patella tendinopathy by distalising tibial tubercle osteotomy

Patella tendinopathy condition is often resistant to conservative treatment. We report a case of patella tendinopathy treated by distalisation of the tibial tubercle with excellent long-term result.

Patella tendinopathy Zoobiquity - What can we learn from dogs?

BACKGROUND

Patella tendinopathy is an overuse condition. Pathogenesis and identification of intrinsic risk factors have largely eluded the orthopaedic world. The cranial cruciate ligament (CrCL) in dogs is the equivalent to the human anterior cruciate ligament (ACL). We report the effect of two canine proximal tibial osteotomy procedures in the veterinary literature on patella tendon moment arm and describe the biomechanical rationale for a tibial tubercle osteotomy for treatment of patella tendinopathy in the human.

METHODS

A literature review of studies reporting clinical complications of TTA and TPLO to form an observational animal cohort study in dogs.

RESULTS

The veterinary literature reports an overall clinical complication rate of up to 61% for TTA and up to 50% for TPLO respectively. Complications associated with the extensor mechanism of the knee are <1% for TTA compared to 1.9-19% for TPLO. Radiographic thickening of the patella tendon and tendinopathy is seen in one to 80% of TPLO cases. The TPLO decreases the moment arm of the extensor mechanism meaning increased force is required in the patella tendon to achieve the same torque when compared to the TTA which increases the efficiency of the extensor mechanism. This difference may account, in part, for the post-operative complications reported to the patella and patella tendon following TPLO.

CONCLUSION

This observational animal cohort study demonstrates a biomechanical rationale for investigating diagnostic and potential treatment options, including a tibial tubercle osteotomy, for patella tendinopathy in humans based on this principle.

Evaluation of Intrinsic Biomechanical Risk Factors in Patellar Tendinopathy: A Retrospective Radiographic Case-Control Series

Background

Patellar tendinopathy is an overuse condition often affecting athletes. It has been postulated that patellar tendinopathy is associated with patella alta; however, this and any other anatomic risk factors have not been identified.

Purpose

To explore whether lever arm differences from radiographic measurements exist between patients with and without tendinopathy. This may provide surgeons with a simple radiographic means to identify patients at risk.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Magnetic resonance imaging scans of the knee from a sports imaging facility were screened and reviewed to identify 2 groups of patients: those with and those without imaging signs of patellar tendinopathy. The lateral radiographs were reviewed and measurements made to determine (1) lever arm ratio, (2) moment arm ratio, (3) angle between the moment and line of pull of the patellar tendon, (4) patellar tendon pivot point angle, and (5) patellar height (alta). Measurements were obtained directly from radiographs. The images and measurements were reviewed by 2 experienced orthopaedic clinicians.

Results

A total of 105 patients were included in this study: 52 with patellar tendinopathy and 53 without patellar tendinopathy (controls). The mean age was similar between groups (23 years); females accounted for 8 of 52 patients with patellar tendinopathy and 24 of 53 patients without. The lever arm ratio in the group with patellar tendinopathy versus controls was 1.71 versus 1.01 (P = .01), with a moment arm difference of 1.00 versus 0.80 (P < .01), respectively. There was no difference detected between groups for patellar tendon angle, patellar tendon pivot point angle, knee flexion angle, or incidence of patella alta. No correlation was found with our measurements and the Insall-Salvati ratio. Statistical analysis was also performed according to sex, and a statistically significant difference between groups was found for differences in lever arm ratio and moment arm.

Conclusion

The lever arm ratio and moment arm ratio from lateral radiographs were significantly different between patients with and without patellar tendinopathy. Further study is needed on the biomechanical implications of the pivot point and how altering it can affect stress within the patellar tendon, patellofemoral joint, and associated clinical outcomes.