Knee impingement syndromes

Patella-patellar tendon angle in relation to the medial patellar plica syndrome, chondromalacia patella, and infrapatellar fat pad syndrome

The patella-patellar tendon angle (PPTA) assessing the sagittal patellar tilt was reported to be related with anterior knee pain. Herein, clinical effect of PPTA in patients with medial patellar plica (MPP) syndrome, chondromalacia patella, and infrapatellar fat pad (IPFP) syndrome, the most common causes of anterior knee pain, was evaluated. In this retrospective study, 156 patients with anterior knee pain who underwent magnetic resonance imaging (MRI) and arthroscopic surgery that confirmed isolated MPP syndrome, chondromalacia patella, or IPFP syndrome from June 2011 to January 2021 were included in the study group and 118 patients without knee pathology on MRI during the same period were included in the control group. The PPTA was measured on knee MRI and compared between the two groups. A receiver operating characteristic (ROC) analysis was used to evaluate the value of PPTA for predicting the risk of patellofemoral joint disorder. The mean PPTA was significantly smaller in study group (138.1 ± 4.2°) than control group (142.1 ± 4.3°) (p < 0.001). However, there was no significant difference in PPTA among the patients with MPP syndrome, chondromalacia patella, and IPFP syndrome. Furthermore, the ROC analysis revealed that the area under curve, sensitivity, and specificity for predicting the risk of patellofemoral joint disorders were 0.696, 70.3% and 57.6%, respectively, at a PPTA cutoff of 138.3°. Therefore, the smaller PPTA may be associated with MPP syndrome, chondromalacia patella, and IPFP syndrome. Furthermore, PPTA could be a predictive factor for the risk of patellofemoral joint disease in patients with anterior knee pain.

Patella-patellar tendon angle decreases in patients with infrapatellar fat pad syndrome and medial patellar plica syndrome

PURPOSE

Infrapatellar fat pad (IPFP) syndrome and medial patellar plica (MPP) syndrome are two recognized causes of anterior knee pain. However, diagnosing these syndromes is challenging without arthroscopic examination. The aim of this study was to evaluate sagittal patellar tilt in patients with IPFP syndrome or MPP syndrome by measuring the patella-patellar tendon angle (PPTA) in affected patients.

METHODS

Eighty-three patients with anterior knee pain who underwent diagnostic arthroscopy that confirmed isolated IPFP or MPP syndrome from 2011 to 2016 were included in this retrospective study. Patients were divided into Group A (IPFP syndrome, n = 44) and Group B (MPP syndrome, n = 39). The control group included 78 patients without knee pathology who underwent magnetic resonance imaging (MRI) of the knee during the study period. Radiographic measurements, including PPTA, IPFP area, patellar height, axial patellar alignment, patellar tilt, sulcus angle, and lateral trochlear inclination, were made on MRI images by two experienced sports medicine orthopedists.

RESULTS

The mean PPTA in each knee-pathology group was significantly smaller than that in the control group (Group A: 137.3° ± 4.9°; Group B: 138.1° ± 3.2°; control group, 141.4° ± 2.9°). There was no significant difference between groups for any other radiographic parameter evaluated.

CONCLUSION

The PPTA was significantly smaller in patients with IPFP syndrome or MPP syndrome than in healthy controls. Therefore, sagittal patellar tilt should be included in the routine evaluation of patients with anterior knee pain. Evaluation of PPTA may help to diagnose IPFP syndrome or MPP syndrome.

LEVEL OF EVIDENCE

Level IV.

Affordance-Based Surgical Design Methods Considering Biomechanical Artifacts

Surgical design in personalized medicine is often based on native anatomy, which may not accurately reflect the interaction between native musculoskeletal tissues and biomechanical artifacts. To overcome this problem, researchers have developed alternative methods based on affordance-based design. The design process can be viewed in terms of action possibilities provided by the (biological) environment. Here, we use the affordance-based approach to address possibilities for action offered by biomechanical artifacts. In anterior crucial ligament (ACL) reconstruction, the design goal is to avoid ligament impingement while optimizing the placement of the tibial tunnel. Although in the current rationale for tibial tunnel placement roof impingement is minimized to avoid a negative affordance, we show that tibial tunnel placement can rather aim to constrain the target bounds with respect to a positive affordance. We describe the steps for identifying the measurable invariants and provide a mathematical framework for the surgery affordances within the knee.

Magnetic resonance imaging of impingement and friction syndromes around the knee

The knee is a complex joint with its function dependent on a combination of osseous and soft tissue structures. Alteration in the relationship of these tissues, due to either acute or chronic repetitive injury with possible underlying congenital predisposing factors, can result in impingement between the structures resulting in pain, particularly on activity. The purpose of this article is to provide a comprehensive review of the MRI features of various impingement syndromes around the knee.

MR imaging of extrasynovial inflammation and impingement about the knee

The knee has unique anatomy regarding the relationship between the synovial and capsular layers, with interposed fat pads at certain locations. The extrasynovial impingement and inflammation syndromes about the knee are underdiagnosed and should be included in the differential diagnosis of anterior knee pain. MR imaging is the best imaging modality for evaluation of the anatomy and disorders of these extrasynovial compartments.

Evaluating anterior knee pain

Musculoskeletal complaints account for about 20% to 30% of all primary care office visits; of these visits, discomfort in the knee, shoulder, and back are the most prevalent musculoskeletal symptoms. Having pain or dysfunction in the front part of the knee is a common presentation and reason for a patient to see a health care provider. There are a number of pathophysiological etiologies to anterior knee pain. This article describes some of the common and less common causes, and includes sections on diagnosis and treatment for each condition as well as key points.

Influence of an infrapatellar fat pad edema on patellofemoral biomechanics and knee kinematics: a possible relation to the anterior knee pain syndrome

INTRODUCTION

An edema of the infrapatellar fat pad following knee arthroscopy or in case of chronic anterior knee pain syndrome is suspected to increase the patellofemoral pressure by a modification of the patellofemoral glide mechanism. The study was performed to evaluate this hypothesis.

MATERIALS AND METHODS

Isokinetic knee extension from 120 degrees of flexion to full extension was simulated on 10 human knee cadaver specimens (six males, four females, average age at death 42 years) using a knee kinemator. Joint kinematics was evaluated by ultrasound sensors (CMS 100, Zebris, Isny, Germany), and retro-patellar contact pressure was measured using a thin-film resistive ink pressure system (K-Scan 4000, Tekscan, Boston). Infrapatellar tissue pressure was analyzed using a closed sensor cell which was implanted inside the fat pad (GISMA, Buggingen, Germany). An inflatable fluid cell was implanted by ultrasound control in the center of the infrapatellar fat pad and filled subsequently with water to simulate a fat pad edema. All parameters were recorded and analyzed from 0 to 5 ml volume of the fluid cell.

RESULTS

Simulating a fat pad edema resulted in a significant (P < 0.01) increase of the infrapatellar fat pad pressure (247 mbar at 0 ml to 615 mbar at 5 ml volume). In knee extension and flexion the patella flexion (sagittal plane) was decreased while we did not find any other significant influence of the edema on knee kinematics. During the analysis of the patellofemoral biomechanics, a simulated fat pad edema resulted in a significant (P < 0.05) decrease of the patellofemoral force between 120 degrees of knee flexion and full extension. The contact area was reduced significantly near extension (0 degree-30 degrees) by an average of 10% while the contact pressure was reduced at the entire range of motion up to 20%.

CONCLUSION

An edema of the infrapatellar fat pad does not cause an increase of the patellofemoral pressure or a significant alteration of the patellofemoral glide mechanism. Anterior knee pain in case of a fat pad edema may be related to a significant increase of the tissue pressure and possible histochemical reactions.

Therapeutic ablation of the infrapatellar fat pad under ultrasound guidance: a pilot study

AIM

To describe the technique of ablation of the infrapatellar fat pad using alcohol injection under ultrasound guidance and to assess the efficacy of the procedure in the relief of pain arising from fat pad impingement.

MATERIAL AND METHODS

Consecutive patients with anterior knee pain and pathology in the infrapatellar fat pad, confirmed on magnetic resonance imaging (MRI), were enrolled in the study. A mixture of alcohol and local anaesthetic was injected under ultrasound guidance, with repeat injections at three-weekly intervals. Twelve patients (seven men, five women), mean age 30.8 years, underwent the procedure. Visual analogue scale pain scores were recorded before treatment and at the end of the treatment course.

RESULTS

Before treatment, the mean (+/-SD) pain score was 7.75 (+/-1.14). Patients underwent a mean of four injections (range 2-6). After treatment, the mean pain score was 2.92 (+/-2.61), representing a decrease of 62% (p<0.001). Follow-up data were complete for all 12 patients. Other than short-lived pain at the time of injection, no serious side-effects were encountered.

CONCLUSION

In patients with pain due to inflammation of the infrapatellar fat pad, ultrasound-guided alcohol ablation of the fat pad can provide effective symptom relief. The results of this pilot study indicate that a larger study is warranted to assess the long-term benefits of this well-tolerated procedure.

MRI of overuse injury in elite athletes

Overuse injuries are a common finding in elite athletes. Magnetic resonance imaging (MRI) is the optimal method for the diagnosis of overuse injury in athletes of all levels. We present a review of common and important overuse injuries occurring in elite athletes. A systematic approach based on the functional anatomic units - tendons, bones and joints - may assist in diagnosis of these injuries.

Prefemoral fat pad: impingement and a mass-like protrusion on the lateral femoral condyle causing mechanical symptoms. A case report

We describe a case of prefemoral fat pad impingement between the anterior aspect of the distal femur and the patella undersurface, and a mass-like fatty tissue protrusion on the lateral femoral condyle that caused mechanical symptoms.

Distribution of substance-P nerves inside the infrapatellar fat pad and the adjacent synovial tissue: a neurohistological approach to anterior knee pain syndrome

INTRODUCTION

The purpose of the study was to determine the distribution and number of nerves inside the infrapatellar fat pad and the adjacent synovium, in particular with regards to nociceptive substance-P nerves.

MATERIALS AND METHODS

The infrapatellar fat pad of the knee was resected from 21 patients (4 male, 17 female, mean age 69 years) during the course of standard total knee arthroplasty operations performed in our clinic. The fat pad was dissected into five standardized segments, fixed in formalin and embedded in paraffin. Immunohistochemical techniques using antibodies against S-100 protein and substance-P (SP) were employed to determine and specify the nerves.

RESULTS

Studying all the detectable nerves present in 50 observation fields (200-fold magnification), we found an average of 106 S-100 versus 25 SP nerves (24%) in the synovium and 27 S-100- versus 7 SP nerves (26%) in the interior of the fat pad. The total nerve count was significantly (P < 0.001) higher in the synovium than in the fat pad for both marker types. The number of S-100 nerves was significantly (P < 0.05) higher in the central and lateral segments of the fat pad, while SP nerves were equally distributed throughout all segments of the fat-pad. SP nerves were significantly more frequently associated with blood vessels inside the fat pad (43%, P < 0.05) than in the synovial tissue (28%).

CONCLUSION

The occurrence and distribution of SP nerves inside the infrapatellar fat pad suggest a nociceptive function and a neurohistological role in anterior knee pain syndrome. The data support the hypothesis that a neurogenous infection of the infrapatellar fat pad could contribute to anterior knee pain syndrome.

Fat-pad impingement after total knee arthroplasty with the LCS A/P-Glide system

Early follow-up (15.8 months;1-48) of 230 knee replacements with an LCS A/P Glide component indicated an increased occurrence of anterior knee pain due to a fat-pad impingement, necessitating early revision surgery. Unsatisfactory results were observed in 28 knees (12.2%). Thirteen knees (5.7%) were revised on finding the fat-pad impingement, and four knees (1.7%) were scheduled for later revision surgery; the remaining 11 subjects (4.8%) had revision surgery for a different reason. Twenty-six subjects (11.3%) complained about milder but typical symptoms of a fat-pad impingement, and 22 subjects (9.6%) had unspecific mild symptoms. 151 knees (65.7%) were free of pain and demonstrated an excellent result. The total revision rate of 10.4% (24 knees) is higher than described for other implant systems. However, the revision needed to treat the fat-pad impingement (5.7%) consisted of minor surgery only, such as exchange of the mobile bearing or reduction of the fat pad by arthroscopy. The femoral and tibial components were able to be left untouched. Resection of the Hoffa's fat pad is recommended when such an implant system is used, and possible impingement should be investigated intraoperatively before closure.

Hoffa's recess in the infrapatellar fat pad of the knee on MR imaging

The infrapatellar fat pad of Hoffa is a structure that is located in the space between the back side of the patellar ligament and the real capsule. It is routinely visualized on magnetic resonance (MR) images of the knee. The purpose of this study was to determine the prevalence and shape of a fluid-like indentation at the inferior posterior margin of the infrapatellar fat pad of the knee (recess) and to look for a relation between the liquid image in the fat pad and joint effusion. Three hundred and fifty consecutive MR imaging examinations of the knee were evaluated for the presence, location, size and shape of a recess in the infrapatellar fat pad and existence of joint effusion. The study population consisted of 145 females and 205 males aged between 5 and 80 years old (mean age 37.5 years). The recess in the infrapatellar fat pad was revealed on MR imaging in 54 of 350 knees (15.43%) and had a variable shape, consisting of 35 linear or ovoid (64.81%), five pipe-shaped (9.26%) and 14 globular (25.92%). Additionally, one ganglion cyst was observed in the infrapatellar fat pad. Globular and pipe-shaped recesses may be confused with cystic infrapatellar fat pad pathologies such as ganglion cyst, meniscal cyst, loose body or nodular synovitis. The existence of an infrapatellar fat pad may not be related to the presence of joint effusion.

MRI of Hoffa's fat pad

The infrapatellar fat pad of Hoffa is commonly injured but rarely discussed in the radiological literature. Abnormalities within it most commonly are the consequences of trauma and degeneration, but inflammatory and neoplastic diseases of the synovium can be confined to the fat pad. The commonest traumatic lesions follow arthroscopy, but intrinsic signal abnormalities can also be due to posterior and superior impingements syndromes and following patellar dislocation. Infrapatellar plica syndrome may also be traumatic in aetiology. The precise aetiology of ganglion cysts is not understood; the principal differential diagnosis is a meniscal or cruciate cyst. Hoffa's fat pad contains residual synovial tissue, meaning that primary neoplastic conditions of synovium may originate and be confined to the fat pad. Inflammatory changes along the posterior border of the pad may also be used to help differentiate effusion from acute synovitis on unenhanced MR examinations.