Case 1: A 68 year-old woman presented with a 1-month history of right medial knee pain following a minor mechanism of stepping on uneven ground. She had unexpected intermittent episodes of sharp knee pain lasting seconds with walking and certain movements. There were no mechanical symptoms or swelling. On examination, she had subluxation of her medial hamstring with passive flexion and extension. There was mild tenderness to the pes anserine tendons. There were no findings indicating meniscal or ligamentous pathology.
Case 2: 35 year old man presents with a several year history of lateral knee snapping following cycling 2 hours/day. There was no report of a specific injury. Patient significantly limited with activity including cycling and running because of the snapping, only asymptomatic with inactivity. Able to reproduce snapping with active flexion and extension of knee. Taping was not effective for this patient. Remainder of knee examination was normal.
Medial knee snapping occurs uncommonly and is infrequently described in literature. Several case reports showed that soft-tissue structures, most commonly the semimembranosus and gracilis tendons (1-4), were responsible for this snapping phenomenon. Lateral knee snapping is also uncommon, biceps femoris tendon can snap over the fibular head when actively being flexed or extended.
Medial: Two studies made speculations as to the underlying cause of this condition. One performed an anatomical study where the investigators found that the affected gracilis tendon was aberrantly located anterior to the posterior edge of the medial femoral condyle (1). Another group of investigators postulated that overloading of the anterior aspect of the knee in jumping sports combined with knee hyperextension increase the force of displacement on semitendinosus and gracilis, causing them to slip out of the shadow groove. This may be accentuated by faulty protective mechanism involving the accessory tendinous expansions of the semitendinosus. These accessory bands prevent the tendon from slipping out and may be less effective the more distally placed they are due to a longer lever arm (2).
Lateral: 18 cases were identified in the literature with three different pathologies. 1) Exotoses, or abnormal fibular head (which anterior portion snaps over) 2) Anatomilcal anomaly – fibular insertion located more anteriorly located fibular head or abnormal tibial insertion. 3) Partial tears of distal tendons. The majority of cases occurred in males (15/18), and in the absence of injury. In 2 of the 18 cases occurred after injury – 2 soccer.
Medial: Medial meniscal tear, Pelligrini stieda lesion, rheumatoid nodules, underlying osteochondroma, osteoarthritis.
Lateral meniscal tears, iliotibial band syndrome, proximal tibiofibular joint instability, popliteus, peroneal nerve compression/neuritis, lateral discoid meniscus, rheumatoid nodules, plica, osteochnodroma, osteoarthritis.(6)
Snapping medial hamstrings typically occur in patient anywhere from the teens to the 30’s, however older patients may also have these symptoms. Symptoms were knee pain and posteromedial snapping with movements involving flexion and extension of the knee. Onset was insidious with no clear preceding trauma. The symptom duration reported was anywhere from 6 months to 17 years on presentation (1-5). As with other snapping tendon syndromes, it they typically occur with a repetitive exercise where the joint is flexed and extended. Our first case eludes to the the potential contributing factor of muscle atrophy.
Lateral snapping hamstrings, in cases identified in literature, occurred between the ages of 15 and 44, in either active patients with history of running, cycling, and/or deep squatting or inactive patients. The condition is occasionally painful, but pain-free snapping is also reported. The snapping often leads the athlete to discontinuing their afffected activity.
Positive physical findings described include palpable and visible snapping observed at the posteromedial aspect at 30 degrees of flexion during active and passive flexion/extension (1,4), and tenderness to the posteromedial area (4).
Snapping Biceps Femoris:
Ultrasound of Tendon snapping:
Medial: Some cases made the diagnosis primarily based on history and physical examination, in the absence of diagnostic imaging findings (1,5). Two papers diagnosed this condition with dynamic ultrasound and advocated for the use of this modality in this context (2,4). One showed that the gracilis and semitendinosus tendons were flicking over the semimembranosus at 30 degrees of flexion as the knee was moved from full flexion to extension and vice versa (4). Another study showed anterior subluxation of the semitendinosus and gracilis tendons over the semimembranosus insertion at the posteromedial corner of the tibia during active terminal extension (2).
Lateral: Clinically the snapping hamstring can be identified on inspection with active flexion and extension of the knee between 70 and 120 degrees of knee flexion (9, 11, 14, 16, 20)
Ultrasound – will demonstrated subluxation, may identifiy tear, or hyperemia in affected tendon.
Xray – may identify increased fibular head size
MRI – can be used to rule out: lateral meniscal tear, discoid meniscus, partial biceps femoris tears, anomalous fibular head/exostosis, popliteus injury
Medial: All case reports reviewed were published in orthopedics literature with subsequent discussion on surgical management. Various techniques including resection or release of the tendons involved were described with positive outcomes reported (2-5).
Lateral: Conservative treatments included hamstring stretching, taping/thigh straps, non-steroidal anti-inflammatories and modification of intensity of activity. The conservative treatments were often described to be unsuccessful. Surgical intervetions included partial resection of fibular head, relocation (either by tunnel or reattachment) of biceps femoris tendon insertion, anterior band resection, anomalous tibial insertion resection. Peroneal nerve protection is essential for surgical cases.
Authors Dr. Su Fei Yu and Dr. Neil Dilworth (Feb 5, 2019)
9 Bansal R, Taylor C, Pimpalnerkar AL. Snapping knee: an unusual biceps femoris tendon injury. Knee. 2005;12(6):458-460.
10 Mirchandani M, Gandhi P, Cai P. Poster 175 bilateral symptomatic snapping knee from biceps femoris tendon subluxation–an atypical cause of bilateral knee pain: a case report. PM R. 2016;8(9S):S218-S219.
11 Date H, Hayakawa 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.
12 Vavalle G, Capozzi M. Symptomatic snapping knee from biceps femoris tendon subluxation: an unusual case of lateral pain in a marathon runner. J Orthop Traumatol. 2010;11(4):263-266.
13 Bernhardson AS, LaPrade RF. Snapping biceps femoris tendon treated with an anatomic repair. Knee Surg Sports Traumatol Arthrosc. 2010;18(8):1110-1112.
14 Guillin R, Mendoza-Ruiz JJ, Moser T, Ropars M, Duvauferrier R, Cardinal E. Snapping biceps femoris tendon: a dynamic real-time sonographic evaluation. J Clin Ultrasound. 2010;38(8):435-437.