Clinical biomechanics of the patellofemoral joint

Anatomic variations of the knee extensor mechanism may result in predisposition to maltracking or instability ofthe patella and quadriceps mechanism. In addition to these anatomic variations, individuals may subject their knees to a wide variety of activities and stresses. Each case of patellofemoral dysfunction, which may range from only anterior knee pain to patellar dislocation, must be considered individually. In the presence of maltracking or patellar instability that is recalcitrant to rehabilitation, there is no single structure which can be surgically altered, repaired, or reconstructed in each case to expect a satisfactory result. The purpose of this article is to describe recent work on the anatomy and biomechanics of the patellofemoral joint to aid the reader in understanding, assessing, and determining the method of treatment most likely to result in improvement in symptoms associated with patellofemoral dysfunction.     

Internal derangements of the knee associated with patellofemoral joint degeneration

The objective of the present study was to evaluate whether internal derangements of the knee joint are associated with patellofemoral joint (PFJ) degeneration. Data were collected prospectively from 1,000 consecutive knee arthroscopies. Chondral lesions were observed in 854 patients, and these patients were included in this study. Patients details (age, sex, duration of symptoms, injuries, and possible mechanism of injury), operative details (types and number of portals, equipment used), intra-articular findings (articular, meniscal and synovial lesions, and stability characteristics) and procedures performed were recorded. Articular lesions were noted on anatomic articular maps of the different functional zones, using a system which presaged the current ICRS system. Using this zoning system, it was easy for the authors to separate the patients with isolated patellofemoral degeneration and arthritis and to do the statistical analysis. Increased incidence of isolated patellofemoral degeneration was noted in patients with synovial shelves, in comparison with patients without shelves (24.7% vs. 15.5%, respectively; P=0.001). Patients with severe patellofemoral maltracking were found to have increased incidence of isolated patellofemoral degeneration in comparison with patients without patella maltracking (64.7% vs. 18% respectively; P<0.001). In conclusion, patellofemoral maltracking and synovial shelves of the knee are highly associated with PFJ degeneration. On the contrary, meniscal tears and ligamentous injuries are associated mainly with degeneration of other compartments of the knee joint and not the PFJ.     

The effect of femoral component rotation on the kinematics of the tibiofemoral and patellofemoral joints after total knee arthroplasty

Purpose  

Complications after total knee arthroplasty (TKA) often involve the patellofemoral joint, and problems with patellar maltracking or lateral instability have sometimes been addressed by external rotation of the femoral component. This work sought to measure the changes of knee kinematics caused by TKA and then to optimise the restoration of both the patellofemoral and tibiofemoral joint kinematics, by variation of femoral component internal–external rotation.     

Comparison of three standard radiologic techniques for screening of patellar subluxations

The presence of many "abnormal" types of PF joints in asymptomatic cases and the frequent unilateral complaints in morphologically symmetric joints indicate that emphasis must be placed on factors that cause "abnormal" PF joints to decompensate, rendering them symptomatic. These factors include hyperlaxity, puberty, overuse, or athletic activities. It is our conviction that full understanding of PF problems needs dynamic, three-dimensional motion analysis of patellofemoral relationships. At the present time these imaging techniques do not exist, as they require more powerful computer capacities. The absence of strict and reliable relationships between radiographic anomalies and clinical symptoms brings two reflections about the treatments in symptomatic cases: It is common sense to treat PPS by conservative methods first. Our study indicates that the goal should be to turn the symptomatic patella into an asymptomatic one, rather than correcting maltracking by vastus medialis training. The high failure rates at long-term follow-up of patellar maltracking correction by surgical methods such as lateral release and tibial tubercle transfer show us that correction of part or all of the anomalies does not always make the symptoms disappear. A nice lesson in humility for the orthopedist.     

Imaging of patellofemoral disorders

Anterior knee pain is a common symptom, which may have a large variety of causes including patellofemoral pathologies. Patellofemoral maltracking refers to dynamic abnormality of patellofemoral alignment and has been measured using plain film, computed tomography (CT) and magnetic resonance imaging (MRI) using static and kinematic techniques. Patellar dislocation is usually transient, but specific conventional radiographic and MRI features may provide evidence of prior acute or chronic dislocation. In addition, chondromalacia patellae, osteochondritis dissecans, patellofemoral osteoarthritis, excessive lateral pressure syndrome, and bipartite patella have all been implicated in causing patellofemoral pain. The imaging and clinical features of these processes are reviewed, highlighting the specific diagnostic features of each condition.     

Tailored tibial tubercle transfer for patellofemoral malalignment: analysis of clinical outcomes

The purpose of this study was to describe the surgical technique, and evaluate and analyze the clinical outcomes of patients who underwent tibial tubercle realignment in our institution. Reported results of tibial tubercle transfer for patellofemoral malalignment vary considerably. Most authors rely mainly on the passive intraoperative patellar tracking test in determining the new location of the tibial tubercle. Conversely, the senior author relocates the tibial tubercle based on the intraoperative active and passive patellar tracking tests and the condition of the patellar articular surface. The medical records of 66 consecutive patients who underwent 80 tibial tubercle relocation procedures due to patellar instability or patellofemoral pain and maltracking were reviewed. Fifty-five patients with 69 operated knees participated in designated follow-ups which were conducted according to a predesigned protocol. The median follow-up was 6.2 years (range 2–13 years). Clinical outcomes significantly improved compared to the preoperative state; 72.5% of operated knees demonstrated good-to-excellent results according to the Lysholm and Karlsson scores, and physical findings supported the positive effect of the procedure. A statistically significant positive correlation was found between clinical outcomes and male gender, the absence of moderate to severe patellar chondral damage, and instability as the dominant preoperative symptom. Postoperative complication rate was low and patients with longer postoperative follow-ups demonstrated better clinical outcomes. The presented method of tibial tubercle transfer provided a good long-lasting surgical solution for patients with patellar instability and patients with patellar maltracking and anterior knee pain. Good prognostic factors included male gender, clinical patellar instability as the dominant preoperative symptom and intact patellar articular cartilage.     

The role of patellar alignment and tracking in vivo: The potential mechanism of patellofemoral pain syndrome

Purpose and method

Lateral patellar malalignment and maltracking are commonly believed to be associated with patellofemoral pain. In the current review, a computerized and manual search of English-language articles was performed using multiple combinations of the following keywords: ‘patellofemoral pain syndrome’ or ‘patellofemoral pain’, and ‘patellar alignment’ or ‘patellar tracking’. The role of patellar alignment and tracking in vivo is discussed via a review of papers regarding the differences in asymptomatic and symptomatic patella. An attempt is made to identify the potential mechanism of patellofemoral pain syndrome (PFPS).

Conclusion

Evidence suggests that symptomatic patella do not consistently demonstrate lateral malalignment or tracking in patellar tilt and translation. Abnormal patellar alignment and tracking may be potential risk factors that are associated with patellofemoral pain. Other contributing factors should be considered in dealing with patellofemoral pain syndrome. Further studies are required to determine what normal patella alignment and tracking is before going on to define how these are altered in subjects with patellofemoral pain. Furthermore, prospective studies are needed to identify the alteration of patellofemoral kinematics, if any, and whether these are the causative factor or the consequence of the patellofemoral pain syndrome, as well as to determine the risk of development of patellofemoral pain syndrome in individuals with and without abnormal patellar tracking.     

Effect of a patellar realignment brace on patellofemoral relationships: Evaluation with kinematic MR imaging

The effect of a newly developed patellar realignment brace was evaluated in 21 patellofemoral joints (19 patients) with patellar subluxation (13 joints with lateral subluxation and eight with medial subluxation) by using active-movement, loaded kinematic magnetic resonance (MR) imaging. Sixteen patellofemoral joints (76%) demonstrated a qualitative correction of or improvement in patellar subluxation (ie, centralization of the patella or a decrease in the displacement of the patella) after application of the brace. Four of the five “failures” occurred in patellofemoral joints that had patella alta and/or dysplastic bone anatomy. These results indicate that the patellar realignment brace was able to counteract patellar subluxation in the majority of patellofemoral joints studied, as shown by active-movement, loaded kinematic MR imaging. This brace appears to be useful for conservative treatment of patients with patellofemoral joint pain secondary to patellar malalignment and maltracking.     

人类髌股关节三维运动规律的研究

本实验通过精密机械式三维位移测量方法，采用１０条新鲜离体人膝关节标本定标加载，分析研究了屈膝过程中的髌股关切运动学及Ｑ角变化对髌股关节运动的影响。结果发现，人类髌股关切具有复杂而有规律性的三维运动特点，对传统认为“髌骨具二维运动”的观点提出了修正。同时发现，Ｑ角异常增大或减小，虽然对髌股运动趋势无显著影响，但可影响髌股运动幅度从而影响髌股稳定性。髌骨的许多特征运动均发生在屈膝３０°之前，髌骨此时也最不稳定，容易受到伤害提示临床手术治疗、护具设计及运动员选材时应予重视。     

Hoffa病与髌骨运动轨迹异常相关性的MRI研究

目的：探讨Hoffa病与髌骨运动轨迹异常的相关性。方法：回顾性分析46例经MRI证实为髌下脂肪垫水肿的Hoffa病患者（病例组）及28例健康体检者（对照组）的MRI及临床资料。病例组中11例行关节镜治疗及病理学检查。在MRI图像上测量5个髌骨运动轨迹参数,包括股骨滑车深度、股骨滑车与胫骨结节的水平距离（TTTG）、髌骨外移度、外侧髌股角（PFA）和InsallSalvati指数。对这5个指标在病例组和正常组问的差异进行统计学分析。结果：Hoffa病的髌下脂肪垫水肿在脂肪抑制T2WI及PDWI序列上显示清晰,均呈高信号改变。病例组及对照组股骨滑车与胫骨结节的距离（TTTG）、外侧髌股角（PFA）和Insall-Salvati指数间的差异有统计学意义（Z值分别为-2．523、-2．261和-2．812,P值均〈0．05）,两组间滑车深度及髌骨外移度的差异无统计学意义（z值分别为-1．025和-0．111,P值均〉0．05）。病例组内出现髌骨外移度（〉3mm）、外侧髌股角（PFA≤0°）和Insall-Salvati指数（〉1．2）异常者较对照组多,两组间差异有统计学意义（X^2值分别为6．917、5．572和9．582,P值均〈0．05）。结论：Hoffa病的主要MRI表现为髌下脂肪垫水肿,MRI是本病的首选检查方法;Hoffa病与髌骨运动轨迹异常间有相关性。     

Combined distal femoral osteotomy (DFO) in genu valgum leads to reliable patellar stabilization and an improvement in knee function

Purpose

Valgus deformities of the lower extremity influence patellofemoral joint kinematics. However, studies examining the clinical outcome after treatment of patellar instability and maltracking due to valgus deformity are rare in recent literature. This study’s purpose is to analyze the clinical results after combined distal femoral osteotomy (DFO) for treatment of patellar instability.

Methods

From 2010 to 2016, 406 cases of patellofemoral instability and maltracking were treated. Twenty cases of recurring (≥?2) patellar dislocations with genu valgum and unsuccessful conservative treatment were included in the study. A radiological analysis was performed, and anteroposterior (AP), lateral and long leg standing radiographs were analyzed, and the leg axis was pre- and postoperatively measured. At least 12 months postoperatively, the clinical leg axis, range of motion (ROM), apprehension sign, Zohlen sign, and J-sign were physically examined. Pain level and knee function were objectified on a visual analogue scale (VAS). The Lysholm, Kujala, and Tegner scores, re-dislocation rate, and patient satisfaction were also examined.

Results

20 combined DFOs on 18 patients with a median age of 23 years (15–55 years) were performed. The preoperative mechanical leg axis was 6.5°?±?2.0° valgus, and the mean tibial tuberosity to trochlear groove (TT-TG) distance was 19.1?±?4.8 mm. All patients reported multiple dislocations. Intraoperatively, 71% presented III°–IV° cartilage lesions, located retropatellarly in 87% and correlating negatively with the postoperative Lysholm score (r?=???0.462, p?=?0.040). The leg axis was corrected by 7.1°?±?2.6°, and in 17 cases, the tibial tubercle was additionally medialized by 10?±?3.1 mm. All patellae were re-stabilized with medial patellofemoral ligament reconstruction. After a median period of 16 (12–64) months, the pain level decreased from 8.0?±?1.4 to 2.3?±?2.1 (VAS p?≤?0.001) and knee function improved from 40.1?±?17.9 to 78.5?±?16.6 (Kujala p?≤?0.001), 36.1?±?19.5 to 81.6?±?11.7 (Lysholm p?≤?0.001), and 2.0 (1–5) to 4.0 (3–6) (median Tegner p?≤?0.001). No re-dislocation was observed.

Conclusion

Combined DFO is a suitable treatment for patellar instability and maltracking due to genu valgum, as it leads to very low re-dislocation rates, a significant reduction of pain, and a significant increase of knee function with good-to-excellent results in the short-term follow-up. However, a high prevalence of substantial cartilage lesions is observed, causing postoperative limitations of knee function.

Level of evidence

IV, retrospective cohort study.

     

Anatomical double-bundle MPFL reconstruction with an aperture fixation

Since biomechanical studies have shown that the medial patellofemoral ligament (MPFL) is the main restraint against lateral patella displacement, reconstruction of the MPFL has become an accepted method of restoring patellofemoral stability and numerous techniques were described. Due to biomechanical examinations and clinical results, an anatomical double-bundle reconstruction of the “sail-like” MPFL is a reasonable method for achieving stability during complete extension and lower flexion degree. This method also serves to avoid rotation of the patella, providing immediate stability throughout the normal range of motion. However, until today, an aperture fixation technique at the patellar insertion with two bundles has not been described previously. This technique can provide an immediate stability to allow an early rehabilitation with full range of motion.     

Tibial tuberosity transfer for episodic patellar dislocation

Numerous surgical techniques have been described to address episodic patellar dislocations. Some of them involve the soft tissues whereas others primarily address a bony correction. Four principal anatomic factors have been identified that increase the risk for episodic patellar dislocations: trochlear dysplasia, patella alta, patellar tilt, and an excessive tibial tubercle-trochlear groove distance. A treatment algorithm has been proposed to correct each of these factors. It includes the tibial tuberosity transfer, which is able to correct both a patella alta and an excessive tibial tubercle-trochlear groove distance. The tibial tuberosity can be transferred distally or medially or more frequently a combination of both. It will realign the extensor mechanism and increase patellofemoral stability. This procedure may be associated with a medial patellofemoral ligament reconstruction in case of excessive patellar tilt or rarely with a trochleoplasty for major abnormal patellar maltracking.     

Treatment of patellofemoralarticular cartilage injuries with autologous chondrocyte implantation

Autologous chondrocyte implantation (ACI) has successfully been used to repair chondral injuries of the knee. Articular cartilage defects of the patella and trochlea represent a class of cartilage lesions of the knee that have recently been considered an increasing indication for treatment with ACI. These lesions often differ from condyae lesions, having a different etiology and coexisting pathologic conditions in the knee associated with them. Patellar and trochlear cartilage lesions are often associated with patellofemoral maltracking. To obtain good results with these cartilage injuries with ACI, it is essential to address the underlying maltracking issues. Additionally, the contours of the patellar and trochlear cartilage differ from that of the condyles, requiring a modification in the standard technique of periosteal attachment used with condylar lesions. Although results of treating trochlear lesions with ACI have shown good results, the initial reports of treating patellar lesions with ACI were diminished compared to condylar lesions. Recognizing and treating the coexisting pathologic conditions and carefully modifying the standard technique of periosteal attachment has resulted in improved results.     

Motor control of the vastus medialis oblique and vastus lateralis muscles is disrupted during eccentric contractions in subjects with patellofemoral pain

BACKGROUND: Inappropriate control of the vastus medialis oblique and vastus lateralis muscles by the central nervous system can contribute to maltracking of the patella. HYPOTHESIS: The activation timing and amplitude of the vastus medialis oblique and vastus lateralis muscles will be different between normal subjects and patients with patellofemoral pain. STUDY DESIGN: Controlled laboratory study. METHODS: Subjects with patellofemoral pain and asymptomatic control subjects performed maximum voluntary knee extension contractions initiated from a flexed and an extended position. The activation timing and amplitude of the vastus lateralis and vastus medialis oblique muscles were quantified from the recorded electromyographic signals. RESULTS: There were no between-group differences in activation timing. The activation amplitude of the vastus medialis oblique and vastus lateralis muscles of the patellofemoral pain subjects was altered to the greatest extent during eccentric contractions and differed significantly from that of control subjects. CONCLUSIONS: The activation amplitudes of the vastus medialis oblique and vastus lateralis muscles of subjects with patellofemoral pain are consistent with a laterally tracking patella during eccentric contractions. Clinical Relevance: The findings suggest the clinical importance of determining whether altered activation patterns are sensitive to rehabilitation, and, if so, if subjective reports of knee joint pain and function parallel changes in the activation patterns as a result of rehabilitation.     

Management of overtight medial patellofemoral ligament reconstruction

The clinical presentation of an overtight medial patellofemoral ligament (MPFL) reconstruction can differ depending on whether it is too tight in extension (extensor lag) or too tight in flexion (anterior knee pain and loss of flexion). We report one clinical case of each presentation. Both cases were treated with a percutaneous release of the graft. After the release, both patients regained a full active range of motion without residual symptoms. These complications demonstrate that the adjustment of the graft tensioning as well as its femoral position are critical steps in MPFL reconstruction. This procedure requires training and experience in order to avoid early complications related to malposition or inappropriate tensioning of the graft. A surgical management for these overtight reconstructions is recommended, as it will restore function and range of motion, and prevent late patellofemoral degeneration.     

Evidence of trochlear dysplasia in patellofemoral arthroplasty designs

Purpose

The design of the trochlear compartment is crucial in patellofemoral arthroplasty (PFA), because 78 % of patients with isolated patellofemoral arthritis present concomitant trochlear dysplasia with patellar maltracking and therefore remain predisposed to post-operative patellar subluxation and dislocation. The study investigated whether current PFA implants are designed with anatomic trochlear parameters such as the sulcus angle, lateral facet height and groove orientation.

Methods

Five trochlear components of commercially available PFA implants were scanned, and the generated three-dimensional surfaces were measured using engineering design software. The mediolateral trochlear profiles were plotted at various flexion angles (0°, 15°, 30° and 45°) to deduce the following variables: sulcus angle, height of lateral facet and trochlear groove orientation.

Results

Four specimens had sulcus angle >144° in the 45° of flexion, and all five specimens had sulcus angle >143° in 30° of flexion. Three specimens had a facet <5 mm high through the entire range of early flexion (0°–30°), and two specimens had a facet <5 mm high beyond early flexion (30°–45°). The trochlear groove was oriented laterally in all specimens (range 1.6°–13.5°).

Conclusion

Current PFA trochlear components are not always designed with anatomic parameters, and some models exhibit characteristics of trochlear dysplasia. Surgeons are therefore advised to implant components with a deep sulcus, particularly in patients with history of patellofemoral disorders, and to adapt the surgical technique and extensor mechanism if the component implanted has a shallow sulcus, to ensure normal patellar tracking.

Level of evidence

III.     

The effects of medialization and anteromedialization of the tibial tubercle on patellofemoral mechanics and kinematics

BACKGROUND: Medialization and anteromedialization of the tibial tubercle are used to correct patellar subluxation in adults. PURPOSE: To compare the effects of the 2 osteotomies on patellofemoral joint contact pressures and kinematics. STUDY DESIGN: Controlled laboratory study. METHODS: Tibial tubercle osteotomies were performed on 10 cadaveric human knees. The knees were tested between 0 degrees and 90 degrees of flexion while dynamic patellofemoral joint contact pressure and kinematic data were simultaneously obtained. Four conditions were tested: normal knee alignment, simulated increased Q angle, postmedialization of the tibial tubercle, and postanteromedialization of the tubercle. RESULTS: An increased Q angle laterally translated the patella, shifted force to the lateral facet, and increased patella contact pressures. Both medialization and anteromedialization partially corrected the abnormal contact pressures. Medialization partially corrected the shift of force to the lateral facet induced by an increased Q angle, whereas the anteromedialization could not. Both medialization and anteromedialization corrected the patella maltracking. CONCLUSION: Medialization and anteromedialization are equivalent in their ability to correct abnormal patellar mechanics and kinematics.     

Allowing one quadrant of patellar lateral translation during medial patellofemoral ligament reconstruction successfully limits maltracking without overconstraining the patella

Purpose

Graft tensioning during medial patellofemoral ligament (MPFL) reconstruction typically allows for lateral patellar translation within the trochlear groove. Computational simulation was performed to relate the allowed patellar translation to patellofemoral kinematics and contact pressures.

Methods

Multibody dynamic simulation models were developed to represent nine knees with patellar instability. Dual limb squatting was simulated representing the pre-operative condition and simulated MPFL reconstruction. The graft was tensioned to allow 10, 5, and 0 mm of patellar lateral translation at 30° of knee flexion. The patellofemoral contact pressure distribution was quantified using discrete element analysis.

Results

For the 5 and 10 mm conditions, patellar lateral shift decreased significantly at 0° and 20°. The 0 mm condition significantly decreased lateral shift for nearly all flexion angles. All graft conditions significantly decreased lateral tilt at 0°, with additional significant decreases for the 5 and 0 mm conditions. The 0 mm condition significantly increased the maximum medial pressure at multiple flexion angles, increasing by 57% at 30°, but did not alter the maximum lateral pressure.

Conclusions

Allowing 5 to 10 mm of patellar lateral translation limits lateral maltracking, thereby decreasing the risk of post-operative recurrent instability. Allowing no patellar translation during graft tensioning reduces maltracking further, but can overconstrain the patella, increasing the pressure applied to medial patellar cartilage already fibrillated or eroded from an instability episode.

     

A clinical study of the biomechanics of step descent using different treatment modalities for patellofemoral pain

Introduction

In the previous study we have demonstrated that in healthy subjects significant changes in coronal and transverse plane mechanics can be produced by the application of a neutral patella taping technique and a patellar brace. Recently it has also been identified that patients with patellofemoral pain syndrome (PFPS) display alterations in gait in the coronal and transverse planes.

Objective

This study investigated the effect of patellar bracing and taping on the three-dimensional mechanics of the knee of patellofemoral pain patients during a step descent task.

Method

Thirteen patients diagnosed with patellofemoral pain syndrome performed a slow step descent. This was conducted under three randomized conditions: (a) no intervention, (b) neutral patella taping, (c) patellofemoral bracing. A 20 cm step was constructed to accommodate an AMTI force platform. Kinematic data were collected using a ten camera infra-red Oqus motion analysis system. Reflective markers were placed on the foot, shank and thigh using the Calibrated Anatomical System Technique (CAST).

Results

The coronal plane knee range of motion was significantly reduced with taping (P = 0.031) and bracing (P = 0.005). The transverse plane showed a significant reduction in the knee range of motion with the brace compared to taping (P = 0.032) and no treatment (P = 0.046).

Conclusion

Patients suffering from patellofemoral pain syndrome demonstrated improved coronal plane and torsional control of the knee during slow step descent following the application of bracing and taping. This study further reinforces the view that coronal and transverse plane mechanics should not be overlooked when studying patellofemoral pain.