To the best of our knowledge, insertional tendinopathy (enthesopathy) of the distal biceps femoris tendon insertion has not been described in the literature. We present a patient with this condition who experienced pain in the posterolateral part of the knee. After an unsuccessful course of physical therapy, surgical debridement of the degenerative tendon led to complete resolution of the symptoms and a return to full sporting activities. The patient was informed that data concerning his case would be submitted for publication, and he provided consent.
A thirty-four-year-old man presented to our clinic with two months of posterolateral right knee pain. The pain had started abruptly after a full day of playing in the surf at the beach. The pain was localized to the posterolateral part of the knee and worsened with deep knee flexion. There were no mechanical symptoms or instability on knee examination, and there was no effusion. Several courses of anti-inflammatory medication did not relieve the pain.
Medical History
The medical history included hypertension, dyslipidemia, and intermittent low back pain. The only prior surgery was an inguinal hernia repair. The musculoskeletal history included a diagnosis of iliotibial band tightness, which had been treated with stretching exercises at home. Three years earlier, he had sustained a torsional injury to the right knee while skiing. A magnetic resonance imaging (MRI) study at that time showed minor lateral meniscal fraying, but no substantial intra-articular pathology. He had been treated with a course of anti-inflammatory medications and physical therapy and had completely recovered.
Physical Examination
The patient was 175 cm tall and weighed 73 kg, with a body mass index of 23.8. The right knee had full active and passive knee motion from 5° of hyperextension to 135° of flexion. There was no knee effusion. The results of Lachman, anterior drawer, and posterior drawer tests were negative. The dial test showed symmetric rotation of the feet at 30° and 90° of flexion. The knee was stable to varus and valgus stress at 0° and 20° of flexion. Tenderness was present over the distal course of the biceps femoris tendon as it inserted onto the fibular head. There was no fibular head instability. The common peroneal nerve was palpable and nontender. The pain was reproduced by deep squatting and resisted hamstring activation. There was no medial or lateral joint-line tenderness. The patellar tracking, tilt, and translation were all normal. Provocative meniscal maneuvers did not elicit pain laterally or medially.
Imaging
Weight-bearing radiographs of both knees were obtained, including a standard anteroposterior view, a posteroanterior view in 30° of flexion, a sunrise view, and a direct lateral view. Right knee alignment was neutral. There were no acute fractures. There was no evidence of degenerative disease. Radiographs showed a fabella bone in both knees (Figs. 1-A and 1-B).
An MRI was obtained, which included fast-spin-echo T2-weighted images in the axial, sagittal, and coronal planes as well as sagittal proton density images. The study revealed mild tendinopathy of the proximal patellar tendon, and an area of increased T2 signal with cystic changes at the insertion of the biceps femoris tendon onto the fibular head (Figs. 1-C and 1-D). These findings were compatible with an insertional tendinopathy of the biceps femoris tendon.
Clinical Course
After the diagnosis of insertional biceps femoris tendinopathy was made, the patient underwent a physical therapy program focused on eccentric strengthening and stretching of the biceps femoris muscle. Local modalities, including deep massage, iontophoresis, and transcutaneous electrical nerve stimulation, were also employed during fifteen therapy sessions over a two-month period. The physical therapist documented that the patient achieved excellent flexibility and full strength of the hamstrings, although the pain persisted.
The patient was evaluated after completion of this program and confirmed that there had been little clinical benefit throughout this course of treatment. The decision was made to explore the distal biceps tendon and perform a diagnostic arthroscopy.
Operative Findings
Diagnostic knee arthroscopy demonstrated a 10 × 10-mm grade-3 chondral lesion of the medial femoral condyle articular cartilage, but no other intra-articular pathology. A curvilinear 4-cm vertical incision, which was centered over the fibular head, was made. The dissection was carried directly down to the biceps femoris tendon. The fibular collateral ligament and the common peroneal nerve were identified and protected. An incision parallel to the biceps femoris was made down to the fibular head through the substance of the tendon. A 1.8 × 1.1-cm segment of degenerative tendon was removed. The tissue was sent for histologic study. Because there was sufficient biceps tendon still attached to the fibular head, reinforcement of the insertion was not needed. The wound was copiously irrigated and closed in layers. The knee was placed in a hinged brace and the patient was allowed to bear weight as tolerated, with crutches for comfort.
Pathology
The excised tendon was reviewed by our pathologists. They found fibrotendinous tissue with marked degenerative changes. There was no acute inflammatory reaction (Fig. 2).
Recovery
The patient was seen in the office for follow-up at one week, one month, three months, and five months. The wounds healed well. By one month, he was biking and running without pain. At three months, he was running three miles and biking twenty miles without difficulty, but still reported mild pain on the lateral side with deep squats. At five months, he was asymptomatic and had returned to full athletic activity.
Tendinopathies occur frequently in recreational and elite athletes. These can occur within the body of the tendon, within the structures surrounding the tendon, or at the insertion of the tendon on bone (the enthesis)1. Each etiology has distinct clinical and management considerations.
Hamstring injuries are common and usually present as pain in the posterior aspect of the thigh. The biceps femoris is the most commonly injured hamstring2. The majority of injuries involve tendinopathy of the ischial origin or intramuscular strain. Injuries of the distal part of the hamstring are comparatively rare. To the best of our knowledge, there are only two case reports of semimembranosus tendon rupture3,4 and one case report of semimembranosus avulsion from the tibial insertion5 in the English-language literature.
Reports of distal biceps femoris pathology are equally scarce. We found a single case series of eleven male athletes with intrasubstance tendinosis of the biceps6. These injuries all occurred proximal to the enthesis and were managed by the excision of degenerative tendon through a large posterolateral incision of the distal part of the thigh. There are also isolated case reports of painful biceps femoris subluxation that resolved with surgical stabilization7-9.
We report a case of enthesopathy of the distal biceps femoris tendon insertion. The cause of this condition is unknown. It is postulated that asynchronous firing of the two heads of the biceps femoris predisposes the muscle to shear strains and makes it more susceptible to injury. Our patient’s history raises the question of whether previous trauma or chronic hamstring tightness could have also contributed to the disease process.
Surgical debridement of the enthesis is technically simple. The biceps has a large insertional footprint, which includes the fibular head, the lateral condyle of the tibia, and the lateral part of the leg fascia. This allows a large cuff of tissue to be safely removed.
The biggest challenge is diagnosing this condition. The differential diagnosis of posterolateral pain in the knee is extensive. Common injuries include lateral meniscal tears, iliotibial band syndrome, and injuries to the posterolateral corner complex. Enthesopathy of the distal biceps femoris tendon insertion is largely a diagnosis of exclusion. Based on our case, we would expect patients to have no varus instability, a normal dial test, and no pain with meniscal provocation. In addition, isolated tenderness over the distal biceps femoris tendon and fibular head, exacerbated by resisted hamstring activation, may help distinguish biceps enthesopathy from other conditions.
Workup should include radiographs to rule out any osseous pathology or malalignment. Following radiographs, an MRI should be performed. MRI is well established as the study of choice to evaluate hamstring complex injuries10. In our case, changes in the distal biceps femoris included increased T2 signal and cystic changes of the tendon insertion. These changes were subtle, but were apparent after discussion between the surgeon and the radiologist. Knowledge of this rare diagnosis will facilitate the interpretation of imaging results.
In our patient, physical therapy provided no benefit. Because the subacute presentation and MRI findings were more consistent with a degenerative tendinopathy than an acute inflammatory tendinitis, a corticosteroid injection was not considered. The decision to proceed with surgery was based on the success of similar procedures for chronic patellar tendinosis11, insertional Achilles tendinosis12, and debridement of the more proximal part of the biceps femoris tendinopathies6.
The need for concomitant arthroscopy in patients with this injury is unclear. We elected to perform arthroscopy in our patient because of the prior MRI, which suggested a lateral meniscal tear. As the clinician becomes more familiar with the diagnosis of distal biceps femoris enthesopathy, it may be reasonable to perform an isolated debridement of the tendon insertion.
In summary, enthesopathy of the distal biceps femoris tendon insertion should be added to the list of diagnoses considered by the orthopaedist in the differential diagnosis of pain in the posterolateral part of the knee. It presents with unique findings on physical examination and MRI changes that are best appreciated if the clinician has a high index of suspicion for this injury. Surgical debridement of the tendon insertion provided an excellent outcome in our patient and should be discussed with patients as a treatment option for this condition.