Plain patellofemoral radiographs

Plain radiographs of the patellofemoral joint can show patellar location, bone shape, trabecular pattern, and articular space thickness. With stress application, stability can be measured. Radiographs may be obtained in the lateral, anterior-posterior, oblique or axial projections, with or without weight-bearing, with or without muscle contraction, with or without stress application to the ligaments, and with the knee in varying degrees of flexion. In addition to trabecular pattern, the lateral radiograph can reveal patellar subluxation, height, or trochlear dysplasia. The axial view is rarely useful until 30° of knee flexion and then may show joint space loss, patellar shift or tilt, and trochlear geometry. Stress radiographs may be required to show how far the patella can be displaced from the trochlea with a given force, and thus, it may be the most accurate method of determining patellar instability. Weight-bearing films may be necessary to show loss of joint space.     

Biomechanics of patellofemoral instability

The patellofemoral joint functions as a complex extensor apparatus with important biomechanical contributions provided by both articular contact and the surrounding soft tissues. The patella must remain relatively stable while tracking along the anterior and distal surfaces of the femur. If there is instability in the coronal plane (subluxation or dislocation) or around the caudocranial axis (tilt), then pain may result. Stability is maintained through the precise interaction of the patellofemoral articulating surfaces, passive and active soft-tissue restraints, and the alignment of the lower extremity. The purpose of this article is to review these biomechanical variables and how they relate to the treatment of patellofemoral instability.     

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.     

Effect of tibial tubercle elevation on patellofemoral compressive force in patellofemoral arthrosis

In this study, the effect of tibial tubercle elevation on the patellofemoral compressive force (PFCF) was investigated in patients with patellofemoral arthrosis. Fifteen (11 women and 4 men) patients who had undergone tibial tubercle elevation were included in the study. The average follow-up was 4.5 years. The mean age of the patients was 59 years (range 34–71 years). They were able to maintain a normal pain-free daily life. Maximal isometric quadriceps force (Q) was calculated by equating the moment generated by this force to the moment of the force measured at the ankle by a modified hand dynamometer. PFCF was calculated from the quadriceps and patellar tendon forces. Statistical analyses were then applied to the measured and calculated quantities. The mean quadriceps force in the operated knee decreased by 20%. Likewise, the mean PFCF was found to be reduced by 30% in the operated knees as compared with the asymptomatic contralateral knees. The above differences in Q and PFCF between the operated knee and the asymptomatic knee were statistically significant (P < 0.05). Therefore, the results of this study do not agree with the previously held view that Q and PFCF increase due to the removal of pain after the elevation operation. It is our contention that comparison of the forces measured preoperatively in a painful joint with the forces that can be attained postoperatively in the pain-free joint can lead to errors in biomechanical evaluations.     

The influence of medial patellofemoral ligament on patellofemoral joint kinematics and patellar stability

Purpose

Retinacular restraints have a critical role in patellar tracking, limiting the movement of the patella in the trochlear groove. The medial patellofemoral ligament (MPFL) is probably the main stabilizer against lateral displacement; few studies are focused on MPFL role on patellofemoral kinematics and patellar stability. The main goal of this in vitro study was to analyse the influence of the MPFL on the kinematics of the patellofemoral joint and patellar stability.

Methods

Using a non-image-based navigation system, kinematics and anatomical data of six fresh-frozen specimens were collected. A passive flexion–extension from 0° to 90° and static acquisitions at 0°, 30°, 60° and 90°, with and without 25 N of lateral load, were performed with intact and resected MPFL with a 60 N axial force applied to the isolated quadriceps tendon. Patellar tilt and shift were analysed.

Results

The MPFL intact state showed a shift in medial direction during the first degrees of knee flexion—that disappeared in MPFL resected condition—followed by a lateral shift, similar to that of MPFL resected condition. Tilt analysis showed that patella rotated laterally until 85° of knee flexion for intact MPFL condition and until 70° for resected MPFL condition and after rotated medially. Static tests showed that patellar stability was significantly affected by MPFL resected condition in particular at 30° and 60°.

Conclusions

The MPFL has an aponeurotic nature. It works as a restraint during motion, with an active role under high stress on lateral side, but with a small contribution during neutral knee flexion. Its biomechanical behaviour under loading conditions should be kept into account when performing surgical reconstruction of this ligamentous structure.     

Conservative treatment of patellofemoral subluxation

As pointed out in the preface of this book, patellofemoral subluxation is probably the most common knee problem seen in many orthopedists' offices today. Whereas the other authors have emphasized the anatomy and diagnosis, this article should serve as a dry but basic instruction on the exercise program that has been used in our clinic. We have had a success rate with this program of approximately 80 per cent. Certainly not all of the 20 per cent that fail require surgery. The classic exercises are quadricep sets, straight leg raises, hip abductors, hip adductors, hip flexors, and hamstring stretches, which have endured the test of time. The prevention of flexion extension activity, such as running the stadium stairs in order to strengthen the quadriceps of the patient with patellofemoral subluxation should be emphasized. Complications of conservative treatment, such as low back pain, iliopsoas tendinitis, and muscle soreness and the treatment of these is described. Finally, the importance of stretching the hamstring muscles is a cornerstone in the treatment of patellofemoral problems. Likewise, a tight IT band can put abnormal stress on the lateral aspect of the patella. In this article I have tried to point out our approach to conservative treatment of patellofemoral subluxation.     

Radiography of the patellofemoral joint

Radiographs of the knee, and especially the patellofemoral joint, are indeed important, but they must be kept inperspective. There is a tendency for the orthopedist to rely too heavily upon the “x-ray.” Perhaps this is natural because we treat so much trauma, and the diagnostic answers, the fracture classification, and even the preferred treatment are often suggested by the initial radiograph. When it comes to patellofemoral disorders, the history, the physical examination, and the initial radiographs assume nearly equal importance, with the physical examination providing perhaps the best information to explain each patient's pathophysiology and to develop a treatment plan. The patellofemoral joint is unique, so its radiographic evaluation will be unique as well. The axial radiograph, which provides the most information, demands that the clinician know exactly what technique was used before an intelligent interpretation can be made. An understanding of the advantages and disadvantages of these different techniques, as well as an appreciation for the various radiographic measurements that separate “normal” from “abnormal,” will make the clinician's task much easier.     

Osteochondritis dissecans of the patellofemoral groove in athletes: unusual cases of patellofemoral pain

Five athletes who developed osteochondritis dissecans in the patellofemoral groove in the course of sports events at high school and college league level are described. They were male athletes complaining of anterior knee pain. When examining young people engaged in violent sports, it is well to remember that they might have osteochondritis dissecans in the patellofemoral groove. Clinically, four of the five patients under discussion were characterized by tight movements of the patella in a direction parallel to its transversal axis. X-ray studies in lateral projections and CT scans provided useful tools for definitive diagnosis, but AP radiography was no help in diagnosis. Release of a tight lateral retinaculum with or without drilling on the degenerated cartilage was effective in the treatment of osteochondritis dissecans of the patellofemoral groove in three of the four patients.     

Complications in patellofemoral surgery

The complexity of patellofemoral morphology, combined with its injuries and degenerative patterns, leads to varied pathologic diagnoses, as well as surgical procedures to address these problems. Surgical procedures in the patellofemoral joint include tibial tubercle osteotomy, medial patellofemoral ligament surgery, soft tissue procedures on the lateral aspect of the patella, trochleoplasty, and patellofemoral arthroplasty. Understanding potential complications related to the various surgical procedures in the patellofemoral joint is critical to successful surgery. The purpose of this article is to discuss potential surgical complications in procedures performed to address patellofemoral pathology and describe ways to avoid these pitfalls.     

Comparison of patellofemoral outcomes after TKA using two prostheses with different patellofemoral design features

Purpose

The purpose of the present study was to compare the clinical and radiographic results after TKA using two prostheses with different sagittal patellofemoral design features, including outcomes related to compatibility of the patellofemoral joint.

Methods

The clinical and radiographic results of 81 patients (100 knees) who underwent TKA using the specific prosthesis (group A) were compared with those in a control group who underwent TKA using the other prosthesis (group B). The presence of anterior knee joint pain, patellar crepitation, and patellar clunk syndrome was also checked.

Results

The function score and maximum flexion angle at the last follow-up were slightly better in group A than those in group B (92.0 ± 2.3 vs. 90.6 ± 4.2) (133.6° ± 8.4° vs. 129.6° ± 11.4°). Anterior knee pain was observed in 6 knees and patellar crepitation in four knees in group A. In group B, these symptoms were observed in 22 knees and 18 knees, respectively. There was no patellar clunk syndrome in either group. The alignment was corrected with satisfactory positioning of components. The patellar height remained unchanged after TKA in the two groups. The differences between preoperative and postoperative patellar tilt angle and patellar translation were small.

Conclusion

When comparing the clinical and radiographic results after TKA using two prostheses with different sagittal patellofemoral design features, TKA using the specific prosthesis provided satisfactory results with less clinical symptoms related to the patellofemoral kinematics with TKA using the other prosthesis.

Level of evidence

III.

     

The influence of cadence and shoes on patellofemoral joint kinetics in runners with patellofemoral pain

Objectives

To determine the effect of a combination of a minimalist shoe and increased cadence on measures of patellofemoral joint loading during running in individuals with patellofemoral pain.

髌股关节排列紊乱的CT测量

髌股关节排列紊乱可导致髌骨力线不正,造成软骨损伤和退变,是导致髌骨软化症和髌股骨关节病的一个重要原因.正确认识髌股关节排列紊乱,有利于临床早期进行治疗并指导患者进行正确的锻炼和运动,从而延缓关节软骨的损伤和退变.本文介绍了髌股关节排列紊乱的常用CT测量方法及其临床价值.     

Technical pitfalls of patellofemoral surgery.

The major technical pitfalls in the performance of patellofemoral surgery stem from improper patient selection, unrealistic patient expectations, and inappropriate rehabilitation. Proper patient selection requires the physician to spend additional time in communicating with patients obtaining a comprehensive history, and performing a thorough physical examination. Patients' expectations can be realistic if appropriate time is devoted to patient education. A commitment on behalf of patients to undertake a comprehensive postoperative rehabilitation program before proceeding with any surgical procedure helps to enhance patients' success.     

The effects of weight-bearing conditions on patellofemoral indices in individuals without and with patellofemoral pain syndrome

Objective

The purpose of this study is to evaluate differences between the patellofemoral joint indices after supine, non-weight-bearing and standing position, and weight-bearing Merchant view radiographs in individuals without and with patellofemoral pain syndrome (PFPS).

Materials and methods

Radiographs of 44 knees without PFPS and 51 knees with PFPS were retrospectively evaluated. In both positions, the non-weight-bearing and weight-bearing Merchant views, patellar indices such as patellar tilt angle, lateral patellofemoral angle, lateral subluxation distance, lateral patellar displacement, and congruence angle were measured, respectively. The differences between the patellofemoral joint indices in knees with and without PFPS were analyzed using univariate and multivariate regression analysis, in regards to correlation factors.

Results

The patellar tilt angle (p?=?0.0002), lateral subluxation distance (p?=?0.038), lateral patellar displacement (p?=?0.0004), and congruence angle (p?<?0.0001) on the weight-bearing Merchant view was significantly decreased in normal knees without PFPS. In pathologic knees with PFPS, the patellar tilt angle (p?<?0.0001), lateral subluxation distance (p?<?0.0001), lateral patella displacement (p?<?0.0001), and congruence angle (p?<?0.0001) on weight-bearing Merchant view was also significantly decreased. The difference between the patellofemoral indices was significantly more in knees specifically with PFPS (p?<?0.05).

Conclusions

These results suggest that patellofemoral indices measured during non-weight-bearing supine position do not sufficiently represent the patellofemoral kinematics during normal weight-bearing activities. We conclude that this study establishes the clinical significance and relevance of assessing the patellofemoral kinematics by weight-bearing, standing Merchant view radiographs, when evaluating patients with patellofemoral problems.     

The patellofemoral kinematics in patients with untreated developmental dislocation of the hip suffering from patellofemoral pain

Purpose

This study reviews the dynamic patellofemoral CT results of 39 patients with untreated developmental dislocation of the hip who are suffering from knee pain.

Method

The mean age of the patients with unilateral developmental dislocation of the hip was 33.3 (±7.9), for bilateral patients 36.2 (±11.3), and for the control group, it was 31.5 (±8.5). While 14 of them were bilateral, 25 were unilateral. The CT results of 24 asymptomatic adult knees served as the control group. The patellofemoral parameters of patients with unilateral and bilateral developmental dislocation of the hip, the control group’s parameters and the effect of femoral anteversion, limb length discrepancy, severity of dislocation, the mechanical axis deviation on patellofemoral parameters were analyzed.

Results

In patients with unilateral untreated developmental dislocation of the hip, although the patella was located more laterally at initial flexion degrees, it was located more medially at 30° and 60° flexion with respect to the control group. For the involved extremity, the PTA angles at 15°, 30°, and 60° flexion were significantly higher than in the control group corresponding to medial patellar tilt. In patients with bilateral developmental dislocation of the hip, the course of the patella during tracking in terms of patellar shift was similar to that of the unilateral patients. The amount of leg length discrepancy and the severity of dislocation, as well as the mechanical axis deviation, did not affect the patellofemoral parameters.

Conclusion

The patients with untreated developmental dislocation of the hip and suffering from knee pain should be analyzed not only for tibiofemoral abnormalities but also for patellofemoral malalignment.

Level of evidence

Case–control study, Level III.     

Surgical complications of the patellofemoral articulation

The complications associated with surgery on the extensor mechanism of the knee were reviewed. These complications may be avoided by being mindful of the importance of patient selection, establishing specific diagnoses, and then carrying out proper surgical procedures. Also reviewed were the complications associated with the extensor mechanism in total knee arthroplasty. Patellofemoral complications are the most common complications of total knee arthroplasty. The importance of precise surgical technique in aligning the extensor mechanism was emphasized. Caution is probably advisable in the use of metal-backed patellar components for the time being. Lastly, the relatively rare, but important, complications of reflex sympathetic dystrophy, infrapatellar contracture syndrome, and patella infra were reviewed.     

Osteochondritis dissecans of the patellofemoral joint

Osteochondritis dissecans of the patellofemoral joint is an uncommon condition that may be the cause of anterior knee pain or crepitus. We present the clinical features of 37 patients with osteochondritis dissecans lesions of the patellofemoral joint (24 on the patella, 13 on the trochlear groove), including two patients with medial trochlear groove lesions, which have not, to our knowledge, been previously reported. The osteochondral lesions involved the convex articular surfaces. The median age of patients when first examined was 15 years, and 54% of patients had open epiphyses. These lesions were more common in male patients than in female patients (four-to-one ratio). Osteochondritis dissecans of the patellofemoral joint can be overlooked unless quality radiographs are viewed with care and, at arthroscopy, both the patella and trochlear groove are assessed. Treatment depends on the symptoms, site, and nature of the lesion and the patient's age. Nonoperative management includes patellar taping and vastus medialis obliquus muscle exercises. Operative intervention is indicated for patients with mechanical symptoms and includes arthroscopy, consisting of chondroplasty and removal of loose bodies, and lateral retinacular release. In this study treatment generally improved the symptoms, but patients with articular cartilage loss had persistent patellofemoral crepitus and discomfort.     

Magnetic resonance imaging of patellofemoral relationships

Patellofemoral relationships were analyzed in 11 patients (13 knees) with patellar dislocation and 15 asymptomatic subjects (15 knees) at 0° and 20° of flexion. The measurements were made from five consecutive axial images through the patellofemoral joint. The six indices measured were lateral patellar tilt (LPT), lateral patellofemoral angle (LPA), lateral patellar displacement (LPD), patella-lateral condyle index (L/PW), congruence angle (CA), and sulcus angle (SA). The reproducibility of the method was evaluated. The difference between the two study groups was more evident at 0° than at 20° of knee flexion. Significant differences were noted between measurements made at different levels of the joint, particularly in the controls. Isometric contraction of the quadriceps muscle lateralized and tilted the patella slightly in both groups. L/PW with and without quadriceps muscle contraction, and LPA with reference to the anterior condyles differentiated between the two study groups most clearly. LPT and LPA with reference to the anterior condyles differentiated the study groups better than LPT and LPA with reference to the posterior condyles. The reproducibility was good except for inter-observer comparison of CA and SA. The use of an imaging plane selected at the midpoint of the patellar articular cartilage increases the sensitivity of the measurements, since it takes into account both the height of the patella and the tendency towards lateralization. These results indicate that patellar tilt is best measured with the LPA index and patellar lateralization with the L/PW index at 0° knee flexion. This study should always include isometric contraction of the quadriceps muscle.     

Early osteoarthritis of the patellofemoral joint

Patellofemoral joint cartilage lesions are associated with a variety of clinical situations including blunt trauma, lateral patella dislocations, or as a secondary development in the setting of abnormal joint loading. There is a need for more clarity on how to best address these lesions. Most specifically, when is it necessary to surgically treat these lesions of the patella and trochlea and which technique to use? This review will focus on the spectrum of patellofemoral disease/injury and their treatment strategies, with special emphasis on cartilage damage and early osteoarthritis. Chapter sections will review the most common scenarios of cartilage damage in the patellofemoral joint, with an attempt to summarize current treatment, their outcomes, remaining challenges and unanswered questions. Level of evidence V.