Delayed diagnosis and treatment of a distal patellar tendon avulsion in an adolescent

Abstract

Distal patellar tendon avulsions are uncommon. While much is known about proximal patella tendon ruptures, there are very few reports to guide treatment of a patellar tendon disruption near the tibial tuberosity. Moreover, delayed diagnosis and treatment presents additional challenges. We present a distal patellar tendon avulsion in an adolescent whereby diagnosis and treatment were delayed due to a distracting nearby contaminated wound. The tendon was separated from post-traumatic scar then repaired back to its native footprint using suture anchors. This report aims to increase awareness of this rare diagnosis as well as provide details about our chosen treatment and rehabilitation protocol.

Background

Extensor mechanism disruption in a skeletally mature patient is usually due to a quadriceps rupture, patella fracture or proximal rupture of the patellar tendon. It is rarely associated with a distal avulsion of the patellar tendon. Moreover, delayed treatment of knee extensor tendon ruptures is associated with suboptimal outcomes. Physical examination to identify incomplete or absent active knee extension is paramount but may be confounded when nearby distracting injuries to the knee are present. A high index of suspicion and advanced imaging are necessary to avoid missed or delayed diagnosis. This report is intended to highlight the above concepts as well as provide surgeons with information regarding the treatment and rehabilitation of this exceedingly rare injury.

Case presentation

The patient is a male adolescent who fell off a motor scooter while on vacation and sustained a right knee extra-articular wound that was intermittently contaminated with gravel. The patient described bracing for impact with a sudden quadriceps contraction as his hyperflexed knee hit the ground. He could not walk afterwards. The ‘backwards L’-shaped skin damage was located just lateral to the midportion of the patellar tendon. On the first and third day after his injury, two separate irrigation and debridement procedures were performed to clear debris from the wound and reapproximate surgically incised skin created to gain access to deep gravel fragments. The treating surgeon noted that the adjacent and visible midportion of the patellar tendon was intact. Postoperatively, the patient was placed in a knee immobiliser and prescribed oral antibiotics. He presented to our clinic to establish care with a healed wound 12 days after the injury. He reported no interval events. On examination, the knee could passively but not actively extend. During active hip flexion there was a 30° extensor lag.

Investigations

The lack of active knee extension was concerning for an undiagnosed disruption of the extensor mechanism. Standard roentgenograms and an MRI were urgently obtained and demonstrated disruption of the distal-most aspect of the patellar tendon and patella alta (figures 1 and 2). The horizontal limb of the skin wound was proximal to the disrupted portion of the patellar tendon.

Figure 1.

Labelled preoperative T1-weighted sagittal MRI demonstrating a complete avulsion of the distal patellar tendon.

Figure 2.

Preoperative T2-weighted sagittal and axial MRI demonstrating a complete avulsion of the distal patellar tendon with associated bony oedema along its footprint.

Differential diagnosis

In adolescent patients, the differential diagnosis for inadequate knee extension includes patella or quadriceps tendon rupture, patella or patellar sleeve fracture, tibial plateau or tibial tuberosity fracture, bucket handle meniscus tear, and more. Patellar tendon disruption with an intact retinaculum can still allow active knee extension but with an obvious extensor lag. Localisation of pain and palpation of a defect may help differentiate between tendinous, bony and intra-articular pathology. Knee radiographs can not only identify a fracture but also imply tendon disruptions if patella alta or patella baja is present. Ultimately, MRI should be obtained when tendinous, cartilaginous or intra-articular aetiologies are suspected.

Treatment

Absent knee extension with radiographic confirmation of extensor mechanism disruption is an indication for surgical repair. Surgery was scheduled for the first elective date (18 days postinjury). An incision was made along the lateral edge of the patellar tendon. The majority of lateral retinaculum was intact. The distal-most aspect of the patellar tendon transitioned into a disorganised/non-linear array of post-traumatic fibrous tissue that attached to the tibial tuberosity (figure 3). A haemostat was used to elevate the patellar tendon off the underlying capsule and soft tissue. The distal fibrous attachment was stronger than anticipated but manual force alone was able to elevate the distal tendon fibres off of the fibrous adhesions located on the proximal aspect of the tibial tuberosity, suggesting the tendon had avulsed and was healing proximal to its native location. There was no more tendon distally, thus direct tendinous repair was not an option. Scar was sharply dissected off the distal tendon fibres. After proximal release of the tendon from recently formed adhesions, the remaining tendon could be elongated to its native location. The tibial tubercle footprint was decorticated with a rongeur to promote bleeding. Three bioabsorbable suture anchors (Zimmer Biomet, Warsaw, Indiana) were placed into the tibial tubercle footprint as an upside-down triangle (such that the repaired tendon would lay flat on bone). The distal patellar tendon was prepared with two rows of Krackow stitch (#2 FiberWire, Arthrex) and reapproximated to its native location (figure 4). Lateral fluoroscopic images of the knee were performed during tensioning to confirm normal patellar alignment. The paratenon and retinaculum were repaired using absorbable suture. The wound was closed in standard fashion. A knee immobiliser was applied and the patient was instructed to remain toe-touch weight-bearing.

Figure 3.

Intraoperative images demonstrating healthy fibres of the patellar tendon (separated from the underlying adhesions) terminating into a disorganised array of post-traumatic scar formation on the tibial tuberosity.

Figure 4.

Anatomical diagram of the injury. The red arrow represents the avulsion force originating from the quadriceps and the green arrow represents the reparative force created by the suture anchors. Figure created by DAG.

Outcome and follow-up

The patient returned to the office 1 week after surgery and was placed in a cylinder cast in full extension for 3 weeks whereby full weight-bearing was allowed. One month postoperatively, the patient was transitioned to a hinged knee brace locked from 0° to 30° with instructions to advance 20° flexion per week and weight-bear as tolerated in the brace (locked in extension during weight-bearing until 6 weeks after surgery then unlocked). At 2 months, the brace was discontinued and outpatient physical therapy began. At 4 months, the patient had full painless range of motion, 95% strength compared with the contralateral knee, and was cleared for all activities. At 12 months, the patient demonstrated symmetric active resisted knee flexion/extension and reported full return to all prior activities including basketball (figures 5 and 6).

Figure 5.

Postoperative X-rays of the right knee (anteroposterior and lateral) demonstrating restoration of patellar height after repair of the distal patellar tendon to its native footprint using suture anchors.

Figure 6.

At 7 months postoperatively the patient demonstrated full knee flexion and extension.

Discussion

Distal patellar tendon injuries are exceedingly rare (especially in an adolescent with a delayed diagnosis) and the paucity of literature available to guide this patient’s treatment and prognosis was our primary reason for publishing this report. In the largest series available, Capogna et al reported six patients with a distal patellar tendon avulsion, but unlike our patient all six had associated ligamentous injuries that required concomitant or staged surgical procedures.¹ Ali Yousef and Rosenfeld² reported three cases within a larger series of adolescent patellar tendon injuries. Cooper and Selesnick³ described their treatment of two intrasubstance tears in professional athletes with intact extensor mechanisms. Finally, the few remaining case reports available were limited in their ability to guide treatment of our patient given a wide variety of ages, surgical techniques and postoperative protocols.^4–6

Due to its limited incidence, the mechanisms associated with distal patellar tendon disruption are unclear. We believe this was more likely a distal patellar tendon avulsion (rather than a missed laceration) given the patient’s certainty that he did not fall on a linear sharp object and the clearly proximal location of the wounds visualised on skin, retinaculum and MRI. It is certainly possible the prior surgeon missed a partial laceration to the tendon, but there was no gravel or cutaneous scar in that location, the patient underwent two separate debridement procedures, and the appearance of post-traumatic scar at the distal edge of the patellar tendon was rippled. Propagation of a partial tendon disruption has been described after bone-patellar tendon-bone graft harvest during anterior cruciate ligament reconstruction.⁷ One limitation of this case report is that we did not send biopsies for histological examination (which could have clarified whether or not the typical features of avulsion were present) and we support this practice in similar scenarios. With regard to aetiology, a common theme among reports is the inconsistent presence of typical risk factors associated with more proximal patellar tendon ruptures, such as young adult age range, sports and/or certain chronic medical conditions (eg, diabetes mellitus). Capogna et al¹ asserted that distal patellar tendon avulsions are often associated with high-energy multiligament injuries and should be clinically approached as if a knee dislocation occurred. In their series of six patients, one patient developed compartment syndrome and another required internal fixation of an associated tibial plateau fracture.¹ Cooper and Selesnick and Lang et al^{3 4} implied that Osgood-Schlatter disease (OSD) is a predisposing condition. However, among three cases described by Ali Yousef and Rosenfeld,² only one had a history of OSD. The relatively high prevalence of OSD in the general adolescent population seems incompatible with the extremely low incidence of distal patellar tendon avulsions. Perhaps similar to our case, Pagdal⁵ described a 58-year-old who sustained their injury while falling off a motorcycle.

None of the available reports about distal patellar tendon avulsions described delayed treatment. Acute surgical repair of patellar tendon ruptures is preferred within days after injury to avoid proximal retraction, post-traumatic adhesions and quadriceps atrophy.^{8 9} Treatment greater than 2 weeks after injury (as with our patient) is considered delayed and associated with potential need for scar tissue release in the subacute phase and eventually quadplasty and/or supplementary tendon graft for neglected cases.^{10 11} Old tears also require longer rehabilitation strategies with suboptimal outcomes such as incomplete knee range of motion, decreased muscle strength and patient-reported outcomes inferior to those treated acutely.¹² Unfortunately, delayed presentation and treatment of patellar tendon ruptures is still common.¹³

Indications for non-operative management of distal patellar tendon avulsions are unclear due to a lack of evidence. Surgical treatment is generally recommended, especially with absent active knee extension on examination. If retinacular fibres are intact or the tendon is scarred down (as in our patient), patients can demonstrate hip flexion with an extension lag at the knee.

Surgical technique should involve identification and preparation of the native tendon for reapproximation to the tibial tuberosity. Debridement should be thorough enough to differentiate poorly functioning post-traumatic scar from native tendon fibres. Treatment of an old tear is more difficult, as seen in our patient, because demarcating healthy tissue can be challenging. If enough native tendon is not available (or in neglected cases), surgeons should perform graft augmentation using one of many described techniques.¹¹ Failure to augment a weak or insufficient amount of tendon can lead to gap formation and/or postoperative failure.¹⁴ Reapproximation of the tendon to its native footprint has been described using suture anchors, transosseous sutures or direct repair with a wire cerclage reinforcement frame. Suture anchors are the most popular and practical method of fixation near the tibial tuberosity.¹ Multiple suture anchors offer the ability to create a large footprint and distribute contact pressures.¹⁵ Biomechanical studies about repair techniques for proximal patellar tendon ruptures suggest suture anchors limit gap formation and enhance failure loads (each by at least 200%) when compared with transosseous suture tunnels.¹⁶

Postoperative rehabilitation for patellar tendon ruptures varies slightly among surgeons, but described protocols mirror the standard postoperative treatment applied to more proximal ruptures, including passive extension, progressive active flexion, and transitioning from toe-touch weight-bearing to weight-bearing as tolerated (usually with the knee fully extended) during the first 6 weeks after surgery. Chloros et al¹⁷ reported a repair similar to ours in a 52-year-old woman but did not describe their postoperative range of motion protocol. Lang et al⁴ reported an excellent outcome in a 65-year-old man after allowing 0°–90° of motion during the first 6 weeks postoperatively, but their repair included semitendinosus graft augmentation. Miyamoto et al⁶ also allowed 0°–90° of motion during the first 4 weeks postoperatively in an 11-year-old boy after primary end-to-end repair with a cerclage wire reinforcement frame.

While our patient’s tear was diagnosed late and required local debridement and scar release, bioabsorbable suture anchors with adjacent Krackow stitches in the tendon were effective at resetting and maintaining tension of the extensor mechanism throughout healing. The patient’s younger age and good preoperative health very likely contributed to his excellent recovery.

Learning points.

• Distal patellar tendon avulsions are exceedingly rare, but possible.

• Clinicians should have a heightened awareness for extensor mechanism disruption when assessing patients with trauma to their knee, as early diagnosis and treatment is imperative to optimise outcomes.

• The most commonly reported techniques for distal patellar tendon avulsion repair include suture anchors with or without tendon graft augmentation.

• Intraoperative steps should include scar debridement, identification of native tendon fibres and restoration of extensor mechanism tension (with or without fluoroscopy since the exact footprint is more difficult to discern than is the distal pole of the patella during proximal ruptures).

• Postoperative rehabilitation concepts can mirror that of more proximal patellar tendon repairs with similar outcomes.

Ethics statements

Patient consent for publication

Obtained.