Alexander J Baur, DO, Research Fellow¹; Ethan C Gazan, MS OMS-2¹; Taylor Anthony, DO, Orthopaedic Surgery Resident²; William H Fang, DO, Orthopaedic Surgery Resident²; John P Walsh, DO, Orthopaedic Surgery Resident²; Randa Bascharon, DO, Orthopaedic Surgery Attending^3
1Liberty University College of Osteopathic Medicine
²Valley Hospital Medical Center
³Valley Hospital Medical Center, Orthopedic and Sports Medicine Institute of Las Vegas

Abstract

Background
Snapping biceps femoris (SBF) is a rare extra-articular cause of lateral knee pain that can closely mimic meniscal pathology.

Case Presentation
We present the case of a 25-year-old recreationally active male with a decade long history of recurrent, atraumatic episodes of painful knee locking associated with lateral joint-line tenderness and a positive McMurray’s. Multiple magnetic resonance imagings (MRIs) across the symptomatic period have each revealed no intra-articular pathology with intact ligaments and menisci. He had a remote history of right knee arthroscopy for medial shelf plica excision without complication. Dynamic physical examination in office demonstrated visible and palpable subluxation of the distal biceps femoris tendon over the fibular head, confirming the diagnosis of SBF.

Conclusion
This case describes an atypical presentation of SBF mimicking lateral meniscus pathology, resulting in delayed diagnosis and multiple unrevealing imaging studies and procedures. In this 25-year-old male, failure to identify intra-articular pathology broadened the differential diagnosis and led to recognition of snapping of the distal biceps femoris on dynamic examination, with successful conservative management resulting in resolution of locking episodes and return to full activity at 6-month follow-up. Recognition of extra-articular sources of mechanical knee symptoms is critical when MRI and arthroscopy are nondiagnostic, as appropriate diagnosis may allow successful management with targeted conservative treatment and help avoid unnecessary interventions.

Keywords: Snapping biceps femoris; Lateral knee pain; Extra-articular knee pathology; Conservative management; Case report

Introduction
Knee pain is among the most common musculoskeletal complaints in athletes, with meniscus injury being a common etiology(1–4). Meniscal tears can be accurately identified through a composite clinical assessment that integrates patient history with a focused physical examination, including mechanical symptoms such as catching or locking, focal joint line tenderness, and a positive McMurray test(5–10). Magnetic resonance imaging (MRI) remains the gold standard for assessing meniscal pathology and provides important diagnostic clarification when clinical findings are equivocal(11–13). 

When intra-articular evaluation fails to identify a source of mechanical symptoms, clinicians should consider common extra-articular causes of knee pain, such as iliotibial band disorders and patellar instability(14)(15). In patients with lateral knee pain and mechanical symptoms, extra-articular snapping of the biceps femoris tendon over the fibular head has been described in case reports and may closely mimic intra-articular pathology(16–20).

Snapping biceps femoris (SBF) is a rare and poorly understood pathology(21–23). Diagnosis is clinical with visible or palpable tendon snapping over the fibular head during active and passive flexion past 90°(18). Etiology is either prominent fibular head morphology or anatomical variation in distal insertion to the lateral tibia condyle(22). Both nonoperative and operative treatments have been described with successful outcomes, and management decisions are individualized based on patient goals and functional requirements(20–23).

This case report describes a patient with snapping of the biceps femoris tendon that simulated meniscal pathology, leading to multiple MRIs and a diagnostic arthroscopy before the correct diagnosis was established. The case highlights the importance of considering extra-articular etiologies in patients with mechanical knee symptoms when both MRI and arthroscopy are unrevealing.

Case Presentation

Current Presentation
A 25-year-old recreationally active male presented to clinic with right knee pain following a transient locking injury. He experienced a sudden, painful locking of the right knee at approximately 90 degrees of flexion without direct impact while playing soccer. The knee remained locked for approximately ten minutes before unlocking while the knee was passively brought to full flexion. He experienced persistent posterolateral knee pain, lateral joint line tenderness, and subjective instability that persisted and led him to present to clinic.

Medical History
At age 16, the patient experienced the first episode of knee locking while playing dodgeball. Acute locking of the knee in approximately 90 degrees of flexion persisted for 12 hours. He presented for local orthopedic examination, and an MRI was ordered. Results showed mild joint effusion in the lateral gutter, a thickened medial plica shelf, and a small osteochondral lesion of the superior lateral patella with intact ligaments and menisci (Figure 1). Medial plica shelf was suspected to be the cause, and he opted to proceed with arthroscopic excision. Operative findings confirmed intact cartilage, menisci, and ligaments, osteochondral lesion was without flap and was stable, and the medial shelf plica was excised without complication (Figure 2). Postoperatively, the patient followed a staged return to sport protocol with the high school athletic department and completed self-directed physical therapy. Symptoms resolved and the patient returned to full athletic activity approximately 12 weeks status post.

Fig 1

Fig 2

Another episode was sustained at age 18 following a slide tackle during soccer. The knee was locked for five days in flexion at approximately 90 degrees before spontaneously unlocking. He received no treatment but modified activity level until subjective instability discontinued. From ages 19-25, the patient remained active and completed all desired activities, including multiple triathlons and running races without knee locking episode or pain. Figure 3 provides a timeline summarizing the patient’s clinical course (Figure 3).

Physical Exam
On examination, the right knee demonstrated full active and passive range of motion with some discomfort. Tenderness over the lateral joint line and the posterolateral aspect of the knee was described as the focal point of discomfort. Varus and valgus stress testing, Lachman, and drawer tests were negative. McMurray testing elicited significant posterolateral pain and discomfort with a palpable catching sensation. There was no effusion or deformity.

Diagnostic Assessment
The initial differential diagnosis included lateral meniscus tear, loose body, and chondral injury in the setting of recurrent mechanical locking, lateral joint line tenderness, and a positive McMurray test. MRI was ordered and revealed intact menisci, cruciate and collateral ligaments. Cartilage surfaces were persevered, but osteochondral lesion was noted on the superior lateral patella (Figure 4). Progression of the lesion was unable to be compared due to lack of prior imaging at the time. No intra-articular pathology was identified.

Given the absence of intra-articular pathology on repeated MRI and prior diagnostic arthroscopy, attention was redirected toward extra-articular sources of mechanical symptoms, including iliotibial band irritation, proximal tibiofibular joint pathology, and snapping of the biceps femoris tendon. During dynamic examination in the office, active and passive knee flexion beyond approximately 90° reproducibly elicited a visible and palpable subluxation of the distal biceps femoris tendon over the fibular head, accompanied by the patient’s characteristic posterolateral pain and catching sensation. This finding confirmed the diagnosis of snapping biceps femoris. The diagnosis was established clinically, as static imaging had failed to demonstrate the dynamic tendon translation responsible for the patient’s symptoms.

Therapeutic Intervention
Following confirmation of SBF, conservative management was selected because the patient did not have persistent function-limiting symptoms between episodes and preferred to avoid surgery. Therapeutic intervention was dictated by the patient and his pain or discomfort during activity. Treatment was broad and focused on decreasing inflammation of the biceps femoris to decrease snapping and prevent a locking episode. Activity modification included decreasing involvement in sports that required repetitive deep knee flexion, specifically cycling. The patient was encouraged to use nonsteroidal anti-inflammatory medications as needed to decrease inflammation of the biceps femoris and control any pain. 

A home exercise program was generated to focus on posterior chain flexibility and strengthening. Staged approaches for hip thrusts, hamstring curls, Romanian deadlifts, and back extensions were included with weighted variations. Unweighted stretching and core strengthening was emphasized to prevent inflammation, ensure trunk stabilization, and prevent tightening of the biceps femoris tendon to reduce snapping. Strengthening exercises for the quadriceps and hip flexors was encouraged to prevent imbalance. 

Follow-Up and Outcomes
Over a nine-year period, the patient experienced recurrent episodes of posterolateral knee pain and mechanical symptoms but remained highly active, participating in recreational soccer, basketball, and distance running, including completion of multiple road races and a triathlon. During this time, persistent concern for intra-articular pathology led to extensive evaluation, including three MRIs and a diagnostic arthroscopy, none of which demonstrated meniscal, ligamentous, or other intra-articular abnormalities.

Following clinical diagnosis of snapping biceps femoris based on dynamic office examination, the patient elected to pursue conservative management. Treatment broadly consisted of activity modification, nonsteroidal anti-inflammatory medication as needed, and a targeted home exercise program. The patient tolerated the targeted at home exercise program well and completed the home exercise program as prescribed without adverse events or complications. At 6-month follow-up, the patient reported no locking episodes, improved pain and a reduction in mechanical symptoms which he attributed to the home exercise program. The patient maintained participation in desired athletic activities without progression to operative intervention.

Discussion
SBF is an uncommon cause of lateral knee pain that can mimic meniscal pathology. In this case, recurrent painful locking with lateral joint line tenderness and a positive McMurray’s test prompted repeated evaluation for a meniscal tear, though imaging and arthroscopy were unremarkable. Ultimately, dynamic examination revealed visible and palpable subluxation of the distal biceps femoris tendon over the fibular head, confirming the diagnosis of SBF.

This case has several strengths. The patient’s clinical course was documented over nearly a decade, including serial imaging, arthroscopic findings, and longitudinal follow-up after diagnosis, allowing clear illustration of the challenges in diagnosis. It highlights how SBF can convincingly mimic lateral meniscal pathology despite negative MRI and arthroscopy, emphasizing the importance of dynamic examination and consideration of extra-articular causes of mechanical symptoms. Limitations are inherent to a single case report, including limited generalizability and the inability to establish causation or define optimal management. Dynamic imaging such as ultrasound was not obtained. 

This presentation underscores the diagnostic challenge for an uncommon diagnosis with limited prior literature. Most reported cases of SBF occur in young, athletic patients with overlapping symptoms with a meniscus tear, often leading to unnecessary imaging or surgical exploration before confirmation of the underlying diagnosis(16–23). The snapping results from abnormal motion of the biceps femoris tendon as it passes over the fibular head during knee flexion and extension(18). Proposed etiologies include a prominent fibular head, anomalous distal tendon insertion to the lateral tibial condyle, or tendon thickening following repetitive trauma(16,17,20,22).

Diagnosis is primarily clinical and relies on dynamic assessment. The snapping can be elicited during active or passive knee flexion beyond 90°, with visual or palpable translation of the tendon over the fibular head(18). Dynamic ultrasound may demonstrate subluxation in real time and can aid confirmation when the physical exam is equivocal(22,24). Management depends on symptom severity and patient preference. Multiple reports have demonstrated successful outcomes with conservative management, including activity modification and physical therapy(22,23). Persistent, function-limiting symptoms may warrant surgical intervention. Saltzman et al. reported successful outcomes following anatomic repositioning and tendon lengthening using a single suture anchor(25). Hadeed et al. described management with partial fibular head resection(26).

This case finds that conservative management with a home exercise program focused on posterior chain flexibility and strengthening may relieve pain and mechanical symptoms associated with SBF. This association has only been described in the literature by Durand-Hill et al. in a case report that included 6-month follow up with symptom mitigation following daily single-leg bridges, single-leg sit-to-stands, and split squats(25). This case supports their findings and reinforces a viable nonoperative treatment for SBF in patients uninterested in surgical intervention. Exercises tailored to strengthen the hamstrings, gluteus muscles, and erector spinae in a measured manner should allow for control of symptoms and mitigate inflammation that increases snapping.

This case underscores the importance of considering SBF in patients with recurrent lateral or posterolateral mechanical knee symptoms, normal or nondiagnostic MRI, and reproducible snapping over the fibula head during flexion beyond 90°. Additionally, we demonstrate that conservative management focused on strengthening the posterior chain may be effective in mitigating pain and mechanical symptoms associated with SBF. Awareness of SBF as a potential source of lateral knee pain can help avoid unnecessary procedures and expedite appropriate management.

Patient Perspective
When I was 16 and my knee first locked, I was amazed at the amount of pain I experienced. I was relieved when I woke up the next morning and could straighten it, and even more relieved when the MRI showed, what we thought was, the problem. After the arthroscopy and recovery went well, I was able to go back to playing the pickup sports I enjoyed. When it locked again at 18 and stayed that way for several days, I was very scared of further damage because I didn’t want surgery again. Even when I was able to run and play sports again, I was nervous. When it locked again, I was worried that I tore my meniscus because the slide tackle twisted my knee. After another MRI and learning that nothing inside was torn, I was relieved for no surgery but frustrated because I still didn’t have an explanation for why it happened again. During the follow up, when he was able to make my knee snap and show it to me, it finally made sense. I was frustrated doctors hadn’t caught it before and I had a potentially unnecessary knee surgery, but I was thankful to have an answer and a plan moving forward.

IRB/ethics: According to institutional policy, case reports involving a single patient do not require Institutional Review Board approval.

Consent for Publication: Written informed consent was obtained from the patient for publication of this case report and all accompanying images. Identifying information has been omitted to protect patient privacy. This study was conducted in accordance with the Declaration of Helsinki.

Conflict of Interest: The authors have no conflicts of interest to disclose related to the subject of this manuscript.

Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

References

1. Mitchell J, Graham W, Best TM, et al. Epidemiology of meniscal injuries in US high school athletes between 2007 and 2013. Knee Surg Sports Traumatol Arthrosc. 2016;24(3):715-722. doi:10.1007/s00167-015-3814-2
2. Patel DR, Villalobos A. Evaluation and management of knee pain in young athletes: overuse injuries of the knee. Transl Pediatr. 2017;6(3):190-198. doi:10.21037/tp.2017.04.05
3. Duong V, Oo WM, Ding C, Culvenor AG, Hunter DJ. Evaluation and Treatment of Knee Pain: A Review. JAMA. 2023;330(16):1568. doi:10.1001/jama.2023.19675
4. Adams BG, Houston MN, Cameron KL. The Epidemiology of Meniscus Injury. Sports Medicine and Arthroscopy Review. 2021;29(3):e24-e33. doi:10.1097/JSA.0000000000000329
5. Solomon DH, Simel DL, Bates DW, Katz JN, Schaffer JL. Does This Patient Have a Torn Meniscus or Ligament of the Knee?: Value of the Physical Examination. JAMA. 2001;286(13):1610. doi:10.1001/jama.286.13.1610
6. Muellner T, Weinstabl R, Schabus R, Vecsei V, Kainberger F. The Diagnosis of Meniscal Tears in Athletes: A Comparison of Clinical and Magnetic Resonance Imaging Investigations. Am J Sports Med. 1997;25(1):7-12. doi:10.1177/036354659702500103
7. Kocabey Y, Tetik O, Isbell W, Atay O, Johnson D. The value of clinical examination versus magnetic resonance imaging in the diagnosis of meniscal tears and anterior cruciate ligament rupture. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2004;20(7):696-700. doi:10.1016/S0749-8063(04)00593-6
8. Mather RC, Garrett WE, Cole BJ, et al. Cost-effectiveness Analysis of the Diagnosis of Meniscus Tears. Am J Sports Med. 2015;43(1):128-137. doi:10.1177/0363546514557937
9. Evans PJ, Bell GD, Frank C. Prospective evaluation of the McMurray test. Am J Sports Med. 1993;21(4):604-608. doi:10.1177/036354659302100420
10. O’Shea KJ, Murphy KP, Heekin RD, Herzwurm PJ. The Diagnostic Accuracy of History, Physical Examination, and Radiographs in the Evaluation of Traumatic Knee Disorders. Am J Sports Med. 1996;24(2):164-167. doi:10.1177/036354659602400208
11. Wang W, Li Z, Peng HM, et al. Accuracy of MRI Diagnosis of Meniscal Tears of the Knee: A Meta-Analysis and Systematic Review. J Knee Surg. 2021;34(02):121-129. doi:10.1055/s-0039-1694056
12. Ryzewicz M, Peterson B, Siparsky PN, Bartz RL. The Diagnosis of Meniscus Tears: The Role of MRI and Clinical Examination. Clinical Orthopaedics and Related Research. 2007;455:123-133. doi:10.1097/BLO.0b013e31802fb9f3
13. Phelan N, Rowland P, Galvin R, O’Byrne JM. A systematic review and meta-analysis of the diagnostic accuracy of MRI for suspected ACL and meniscal tears of the knee. Knee Surg Sports Traumatol Arthrosc. 2016;24(5):1525-1539. doi:10.1007/s00167-015-3861-8
14. Safran MR, Fu FH. Uncommon Causes of Knee Pain in the Athlete. Orthopedic Clinics of North America. 1995;26(3):547-559. doi:10.1016/S0030-5898(20)32015-0
15. Rosenthal MD. Clinical testing for extra-articular lateral knee pain. A modification and combination of traditional tests. N Am J Sports Phys Ther. 2008;3(2):107-109.
16. McNulty M, Carreau J, Hendrickson N, Bollier M. Case Report: Snapping Biceps Femoris Tendon Due to Abnormal Fibular Morphology. Iowa Orthop J. 2017;37:81-84.
17. Hernandez JA, Rius M, Noonan KJ. Snapping knee from anomalous biceps femoris tendon insertion: a case report. Iowa Orthop J. 1996;16:161-163.
18. Lokiec F, Velkes S, Schindler A, Pritsch M. The snapping biceps femoris syndrome. Clin Orthop Relat Res. 1992;(283):205-206.
19. Kristensen G, Nielsen K, Blyme PJH. Snapping knee from biceps femoris tendon A case report. Acta Orthopaedica Scandinavica. 1989;60(5):621-621. doi:10.3109/17453678909150135
20. Date H, Hayakawa K, Nakagawa K, Yamada H. Snapping knee due to the biceps femoris tendon treated with repositioning of the anomalous tibial insertion. Knee surg sports traumatol arthrosc. 2012;20(8):1581-1583. doi:10.1007/s00167-011-1778-4
21. Reid L, Mofidi A. Bilateral snapping biceps femoris tendon: a case report and review of the literature. Eur J Orthop Surg Traumatol. 2019;29(5):1081-1087. doi:10.1007/s00590-019-02392-9
22. Zadeh C, Khoury N, Najem E, Moukaddam H. Snapping of bilateral biceps femoris tendons: A case report and brief review. Radiology Case Reports. 2022;17(4):1293-1299. doi:10.1016/j.radcr.2021.12.058
23. Durand-Hill M, Dawson A, Odeh O, Spicer D. Snapping Biceps Femoris Syndrome: A Case Presentation and Review of Current Literature. Cureus. Published online September 18, 2024. doi:10.7759/cureus.69688
24. Guillin R, Mendoza‐Ruiz JJ, Moser T, Ropars M, Duvauferrier R, Cardinal E. Snapping biceps femoris tendon: A dynamic real‐time sonographic evaluation. J of Clinical Ultrasound. 2010;38(8):435-437. doi:10.1002/jcu.20728
25. Saltzman BM, Collins MJ, Arns TA, Forsythe B. Unilateral Snapping Biceps Femoris Tendon with an Anomalous Insertion Treated with Anatomic Repositioning and Lengthening with a Single Suture Anchor: A Report of Two Cases. JBJS Case Connector. 2018;8(1):e13-e13. doi:10.2106/JBJS.CC.16.00251
26. Hadeed MM, Post M, Werner BC. Partial Fibular Head Resection Technique for Snapping Biceps Femoris. Arthroscopy Techniques. 2018;7(8):e859-e862. doi:10.1016/j.eats.2018.04.008