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

Friction Syndromes of the Knee

The knee is a complex joint with many fascial and ligamentous interactions. The movement in multiple planes makes the knee a prime site for friction syndromes, especially in active individuals. The most common friction syndrome is the iliotibial band friction syndrome. This occurs commonly in runners and cyclists and can be diagnosed clinically in a patient with lateral knee pain during activity. The anterior fat pads of the knee can also be the site of friction syndromes, most often in the Hoffa fat pad. Edema here can be located in the superolateral aspect of the fat pad when associated with patellar abnormalities, or diffusely when impingement is due to other causes. Edema of the quadriceps or prefemoral fat pad may also cause anterior knee pain and may be diagnosed with magnetic resonance imaging. The posteromedial friction syndrome and medial tibial crest syndrome are rare causes of medial knee pain highly active individuals.

Hyperechoic and Low Morphological Changes in the Prefemoral Fat Pad in Individuals with Knee Osteoarthritis Based on Ultrasonographic Findings

Background:

To clarify the changes in the echo intensity (EI) in the prefemoral fat pad (PFP) and identify the relationship between the PFP and clinical features of knee osteoarthritis (OA).

Methods:

Twenty-six women with knee OA (mean age: 76 years) and 17 healthy women (mean age: 73 years) were enrolled. The Kellgren and Lawrence grading scale was used for the radiographic evaluation of knee OA. The EI of the PFP was measured as grayscale values. The change ratio of the anteroposterior PFP length during quadriceps contraction was measured. Knee range of motion and pain (100-mm visual analog scale) were evaluated.

Results:

The EI was significantly higher in the OA group than in the healthy group (P < 0.001). The change ratio of the PFP in the OA group was significantly lower than that in the healthy group (P < 0.001). The ranges of knee flexion and extension were correlated with the EI of the PFP (both P < 0.01) and the change ratio of the PFP (both P < 0.01). There was no significant correlation observed with knee pain.

Conclusion:

Hyperechoic changes and a decreased change ratio of the PFP were observed in the patients with knee OA. High EI and decreased morphological PFP changes were associated with decreased ranges of motion.

A Case of Prefemoral Fat Pad Impingement Syndrome Caused by Hyperplastic Fat Pad

Case

We report a rare case of prefemoral fat pad impingement syndrome that was caused by a hyperplasia of the normal suprapatellar fat pad. Pain and catching were observed in the proximal-lateral patellofemoral joint, and MRI imaging confirmed a hyperplasic mass in the same area. Although conservative treatment showed no signs of improvement, symptoms improved after an arthroscopic excision of the mass.

Conclusion

Prefemoral fat pad impingement syndrome is related to patellar motion and should be considered as one of the underlying causes of anterior knee pain (AKP). Surgeons should recognize that a small hyperplasia composed of normal adipose tissue can cause AKP.

MRI Findings Consistent with Peripatellar Fat Pad Impingement: How Much Related to Patellofemoral Maltracking?

Peripatellar fat pads are intracapsular extrasynovial adipose cushions that accommodate the changing shape and volume of articular spaces during movement. Variations in bone geometry, passive and active stabilization mechanisms and/or functional demands may lead to peripatellar fat pad abnormalities. While peripatellar fat pads may be affected a variety of conditions such as synovial inflammation, tumor and fibrosis, a mechanical origin should also be considered. Commonly, the clinical term "impingement" is used synonymously in the radiological literature to refer to three distinct entities of structural peripatellar fat pad abnormalities: superolateral the infrapatellar fat pad (Hoffa fat pad) edema, suprapatellar fat pad edema, and prepatellar fat pad edema, implying a mechanical origin of these conditions. The aim of this pictorial review is to describe the normal anatomy of the extensor mechanism of the knee, and discuss the relation of patellofemoral maltracking to the above-mentioned peripatellar fat pad conditions based on current evidence.

Ultrasonographic Morphological Changes in the Prefemoral Fat Pad Associated with Knee Osteoarthritis

Background

In normal knees, quadriceps contraction changes the shape of the prefemoral fat pad (PFP). However, in persons with knee osteoarthritis (OA), the functional or morphological changes of the PFP are unclear. This study aimed to clarify the morphological changes in the PFP in individuals with knee OA through ultrasonography.

Materials and Methods

Participants were divided into the OA (36 knees; mean age, 74 years), elderly (31 knees; mean age, 70 years), and young (26 knees; mean age, 21 years) groups. The anteroposterior (AP) length of the PFP before and during isometric quadriceps contraction at 0°, 30°, 60°, and 90° knee flexion was measured ultrasonographically. The difference between the maximum and minimum length values, change in length, was also measured. These parameters were compared among the three groups. In the OA group, correlations between the parameters and clinical features (knee pain; visual analog scale, knee range of motion [ROM], Kellgren and Lawrence (K/L) grade, and intercondylar distance) were examined by Spearman and Pearson's correlation coefficient tests.

Results

The AP lengths of the PFP before contraction were significantly lower in the OA group than in elderly group and young group at 30° (6.9 ± 2.5 vs. 12.0 ± 3.6 or 11.1 ± 2.7 mm, respectively; in order P = 0.014, P = 0.006) and 60° (6.5 ± 2.0 vs. 9.7 ± 2.5 or 9.1 ± 2.7 mm, respectively; both P < 0.001). The AP lengths of the PFP during contraction were significantly lower in the OA group than in elderly group and young group at 0° (6.7 ± 2.3 vs. 8.8 ± 3.7 or 9.1 ± 1.6 mm, respectively; both P < 0.001), 30° (7.9 ± 2.6 vs. 12.9 ± 3.7 or 13.0 ± 2.6 mm, respectively; both P < 0.001), and 60° (7.1 ± 2.5 vs. 13.5 ± 2.6 or 13.6 ± 3.0 mm, respectively; both P < 0.001). The change in length before maximum isometric quadriceps contraction was significantly lower in the knee OA group than in both elderly and young groups (3.3 ± 1.9 vs. 8.4 ± 2.5 or 6.8 ± 3.0 mm, respectively; both P < 0.001). The change in length during contraction was also significantly lower in the knee OA group than in both the elderly and young groups (3.9 ± 2.3 vs. 8.7 ± 2.3 or 8.9 ± 2.0 mm, respectively; both P < 0.001). In the OA group, change in length during contraction was significantly associated with knee pain (r = -0.476, P = 0.007), knee ROM (r = 0.388, P = 0.019), and Kellgren and Lawrence grade (r = -0.357, P = 0.045).

Conclusions

In knee OA, movement of PFP was decreased more than healthy participants. In the knee OA group, the decrease of the morphological change of the PFP showed the relationship between VAS score, knee extension ROM, intercondylar distance (ICD), and K/L grade. An evaluation to the PFP may be required in individuals with knee OA.

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.

Expected prevalence from the differential diagnosis of anterior knee pain in adolescent female athletes during preparticipation screening

CONTEXT

Anterior knee pain is a common disorder in female athletes with an undefined cause. The relative prevalence of specific patellofemoral disorders associated with anterior knee pain in adolescent females remains undetermined.

OBJECTIVE

To determine the prevalence of specific patellofemoral disorders obtained using the differential diagnosis of anterior knee pain in adolescent female athletes during preparticipation screening.

DESIGN

Descriptive epidemiology study.

SETTING

Preparticipation screening evaluations at a county public school district in Kentucky.

PATIENTS OR OTHER PARTICIPANTS

A total of 419 unique middle and high school-aged female athletes.

MAIN OUTCOME MEASURE(S)

Participants were evaluated by physicians for anterior knee pain over 3 consecutive basketball seasons. Given the longitudinal nature of this study, some participants were tested longitudinally over multiple years.

RESULTS

Over the course of 3 basketball seasons, 688 patient evaluations were performed. Of these, 183 (26.6%) were positive for anterior knee pain. A statistically significant difference was noted in the prevalence of anterior knee pain by school level, with 34.4% (n = 67) in high school-aged athletes versus 23.5% (n = 116) in middle school-aged athletes (P < .05). In the 1376 knees evaluated, patellofemoral dysfunction was the most common diagnosis, with an overall prevalence of 7.3% (n = 100). The only diagnosis shown to be statistically different between age levels was Sinding-LarsenJohansson disease or patellar tendinopathy, with 38 cases (9.7%) in high school-aged and 31 (3.1%) in middle school-aged athletes (P < .05).

CONCLUSIONS

Anterior knee pain was present in 26.6% of the adolescent female athletes screened over 3 years. Symptoms of anterior knee pain likely persist after middle school-aged onset and reach peak prevalence during the high school years.

Suprapatellar fat pad inflammation in step aerobics athletes: MR imaging evaluation of two cases

Step aerobics is one of the most popular exercises with established benefits to cardiovascular status. This activity is associated with injuries which include patellar or talar chondral lesions, quadriceps tendinopathy, Achilles tendinopathy or tear, shin splints and muscle soreness. The purpose of this case report is to present two step aerobics athletes, suffering from anterior knee pain. We observed that their knee MR examination disclosed only suprapatellar fat pad edema. No other findings were noticed. In addition, we discuss the possible pathogenetic mechanism of this entity which has not been previously reported in the literature.