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RFS – Teaching Images

One Year of Knee Pain in a 21-Yr-Old Male Frisbee Player

Zelinger, Perry MD; Pastorius, Daniel DO; Stokes, Wayne MD

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American Journal of Physical Medicine & Rehabilitation: January 2020 - Volume 99 - Issue 1 - p e1-e2
doi: 10.1097/PHM.0000000000001198
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A 21-yr-old male ultimate Frisbee player presented with a 1-yr history of right knee pain. He stated that the pain was around the anterolateral superior aspect of his right patella that was worse with activity and he also had intermittent fullness. He reported a remote history of trauma and knee pain several years ago while playing ultimate Frisbee that resolved spontaneously. He denied swelling, locking, buckling, or instability of the knee. His pain did not prohibit him from continuing to be active.


The results of physical examination are as follows: vitals stable, in no acute distress; no right knee joint effusion; tenderness to palpation at the superior lateral aspect of the patella only; 5/5 strength of the bilateral lower limbs and full active range of motion; negative McMurray's, Lachman's, valgus, and varus stress test; and able to do a full squat without pain.

Differential Diagnosis:

  1. Patellofemoral pain syndrome
  2. Iliotibial band syndrome
  3. Meniscal injury
  4. Lateral collateral ligament strain
  5. Quadriceps tendinopathy
  6. Patellar stress fracture


Plain film revealed bipartite patella with mild marginal osteophytes at the lateral aspect (Fig. 1). In-office ultrasound also revealed degenerative changes at the bipartite patella and cortical irregularity of the deep surface of the patella laterally. Magnetic resonance imaging of the knee showed bipartite patella morphology with sclerosis and cystic changes around the synchondrosis margins (Fig. 2). It also revealed an incidental nondisplaced subchondral impaction fracture of the anterolateral tibial plateau with associated bone marrow edema.

X-ray AP weight bearing of bilateral knees showing bipartite patella on right with mild marginal osteophytes at the lateral aspect. Multipartite patella seen on the left knee.
Coronal proton density fat suppressed magnetic resonance imaging of the right knee showing bipartite patella with mild cystic change, sclerosis and bone marrow edema around the synchondrosis.


The diagnosis is painful degenerative changes of synchondrosis of bipartite patella.


Bipartite patella is a normal anatomic variant seen in between 0.2% and 5% of the population caused by failure of secondary ossification centers to fuse.1 It is usually asymptomatic and incidentally discovered but can present with knee pain after direct trauma (with potential fracture or separation) or from overuse injury. Magnetic resonance imaging studies suggest that bony edema near the synchondrosis can help differentiate bipartite patella as a primary cause of knee pain from other painful knee disorders.2,3 Treatment options are varied and include conservative management such as restriction of activities, immobilization, bracing, physical therapy, medications, and local injections, as well as surgical options including arthroscopic or open bipartite fragment removal, open reduction and internal fixation, and soft tissue releases such as lateral retinacular or vastus lateralis release, all of which have provided good results.4 Most patients can return to normal activity without symptoms after surgical treatment.5

Interestingly, this patient was also found with a tibial compression deformity; however, his pain was localized to the region of the bipartite segment and had no tenderness to palpation over the tibial plateau. His left knee also demonstrated a multipartite patella with three segments, which was asymptomatic.


Patient was referred for surgical evaluation and clearance before starting physical therapy. He received an intra-articular knee injection with triamcinolone and lidocaine, which resulted in complete resolution of his symptoms at 6-week follow-up and allowed gradual increase in his activity level.

The teaching points are as follows:

  • Bipartite patella is a normal anatomic variant seen in 0.2%–5% of people and is often asymptomatic and incidentally discovered; however, it can present with anterior knee pain
  • Magnetic resonance imaging findings of bony edema at the synchondrosis suggest bipartite patella as the primary cause of knee pain
  • Painful bipartite patella responds well to conservative as well as surgical intervention


1. Oohashi Y, Koshino T, Oohashi Y: Clinical features and classification of bipartite or tripartite patella. Knee Surg Sports Traumatol Arthrosc 2010;18:1
2. Kavanagh EC, Zoga A, Omar I, et al: MRI findings in bipartite patella. Skeletal Radiol 2007;36:209–14
3. O'Brien J, Murphy C, Halpenny D, et al: Magnetic resonance imaging features of asymptomatic bipartite patella. Eur J Radiol 2011;78:425–9
4. McMahon SE, LeRoux JA, Smith TO, et al: The management of the painful bipartite patella: a systematic review. Knee Surg Sports Traumatol Arthrosc 2016;24:2798–805
5. Matic GT, Flanigan DC: Return to activity among athletes with a symptomatic bipartite patella: a systematic review. Knee 2015;22:280–5
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