Posterior Cruciate Ligament Agenesis Requiring Surgical Reconstruction

Abstract

Agenesis of the posterior cruciate ligament (PCL) is a rare disorder often found in conjunction with various other abnormalities within the knee. A 15-year-old adolescent boy presented with an absent PCL, leading to intermittent symptoms. At the age of 20 years, the patient underwent arthroscopically assisted PCL reconstruction. The patient was permitted to weightbear immediately after the procedure and started physical therapy 4 weeks after the procedure. No complications were encountered at the 2-year follow-up.

Agenesis of the posterior cruciate ligament (PCL) is a rare disorder most frequently seen in conjunction with agenesis of the anterior cruciate ligament as well as with developmental abnormalities of the surrounding bone. There are few publications that identify cruciate ligament deficiencies and fewer with isolated PCL agenesis requiring reconstruction. This study discusses the case of a patient with chronic intermittent symptoms associated with PCL agenesis that eventually required surgical intervention.

Case Presentation

The patient was initially seen at age 15 years for atraumatic right knee swelling and pain after a basketball game. The patient had no known history of congenital or developmental abnormalities before presentation. The patient had a history of an episode of bilateral knee pain from playing basketball at the age of 13 years, which resolved with bracing treatment and an episode of left (contralateral) knee pain at the age of 14 years after a hike for which a left knee MRI was done, demonstrating no abnormalities. The patient's mother reports a personal history of a meniscus injury treated surgically, but the patient has no other known family history of similar conditions.

On initial presentation, the patient was found to have positive medial joint line tenderness, tibial sag sign, posterior drawer test, quadriceps active test, dial test at 30° of knee flexion, and a positive click with McMurray testing. Over the course of the next 6 years, the patient continued to have intermittent medial joint line pain and evidence of PCL deficiency, including the posterior sag sign, posterior drawer test, and quadriceps active test. The pain was treated nonsurgically with bracing treatment and physical therapy aimed at strengthening and neuromuscular reorientation. The patient continued to experience five episodes of knee pain with full resolution between episodes. Three MRI examinations were done over 6 years (Figures 1 and 2), demonstrating an absence of the PCL without evidence of meniscal derangements and a mildly hypoplastic lateral tibial spine, which was likely a product of the congenitally absent PCL.

Figure 1.

Coronal MRI slice of the right knee demonstrating a lack of posterior cruciate ligament.

Figure 2.

Sagittal MRI slice of the right knee demonstrating a lack of posterior cruciate ligament.

At the age of 20 years, the patient returned to clinic with a new episode of knee pain and a desire to pursue surgical intervention. Joint decision was made to undergo PCL reconstruction given his recurrent episodes of pain, recalcitrant to conservative management. Arthroscopically assisted PCL reconstruction was done using an Achilles tendon allograft with interference screw fixation for both the femur and the tibia (Figures 3–5).

Figure 3.

Arthroscopic view of the right knee demonstrating absent posterior cruciate ligament with intact anterior cruciate ligament.

Figure 5.

Arthroscopic photograph showing the right knee with the reconstructed posterior cruciate ligament.

Figure 4.

Arthroscopy photograph of the right knee demonstrating the empty attachment site for the posterior cruciate ligament.

The patient was placed into a knee range of motion brace locked in extension, which was unlocked 4 weeks postoperatively and physical therapy was started.

At the patient's follow-up visits, he reported continued improvement and a more stable feeling knee. He recovered fully without any adverse events or recurrent episodes of knee pain over the subsequent 2 years of follow-up.

Discussion

Agenesis of the PCL in isolation is a rare phenomenon.^1,2,3,4 It is more commonly associated with other abnormalities, including tibial spine hypoplasia, femoral condyle hypoplasia, meniscofemoral ligament hypoplasia/hyperplasia, fibular hemimelia, and meniscal abnormalities.^5,6,7,8 A classification system has been established for cruciate ligament agenesis but does not account for agenesis of the PCL alone.⁹ There are conflicting theories regarding the etiology, ranging from genetic copy number variation because of a deletion of the CEP57L1 exon to embryological errors during the development of the cruciate ligaments in the 7th to 12th weeks of life in utero.^{10,11,12,13,14,15,16,17,18}

Clinically, PCL agenesis can be found incidentally or present with symptoms of instability.^19,20 Patients may have compensation from other ligaments and muscles to assist with the biomechanical stability in the knee, including thickening of the meniscofemoral ligaments.^19,21 Many authors argue that the congenital absence of the cruciate ligaments is well tolerated. Owing to a paucity of literature, treatment options vary, but most clinicians elect for physical therapy with surgical intervention reserved for refractory symptoms.^{12,22,23,24,25} Some reports of surgical intervention for reconstruction of cruciate ligament agenesis may be fraught with technical difficulties and a high percentage of failure or poor results.² In our review of the literature, we found four case reports that detailed incidental findings of isolated PCL agenesis in patients who presented with knee pain and clinic findings of positive posterior drawer testing. In all four of these cases, the patients were found to be adults and treated conservatively with successful resolution of symptoms.^1,2,3,4 Our case differed in that our patient had symptomatic pain starting from childhood and continuing despite repeated courses of physical therapy. Our case suggests that a patient who demonstrates continued instability and recurrent symptoms over time may require surgical intervention because the presence of continued symptoms could indicate medial joint space wear from altered biomechanics and accelerated development of arthritis.^2,20,23

Our patient experienced repeated recurrence of symptoms with associated laxity found on careful examination, leading to discussion regarding the options for surgical intervention. Given his active lifestyle and refractory symptoms, decision was made to pursue surgical intervention with arthroscopically assisted PCL reconstruction. During the procedure, the patient was found to have PCL agenesis associated with a hypoplastic lateral tibial spine with normal anterior cruciate ligament, meniscofemoral ligaments, and no signs of notable knee trauma. There is a paucity of literature on PCL agenesis, and we are unaware of any literature describing PCL reconstruction for isolated PCL agenesis. The 2-year follow-up showing improvement in the patient's symptoms suggests that careful physical examination should be completed in the setting of PCL agenesis and treatment should be on an individual basis. Surgical intervention and nonsurgical intervention can both lead to successful treatment outcomes depending on the patient's lifestyle and symptoms. It is the opinion of the authors that surgical intervention should be reserved for those with persistent or recurrent symptoms despite adequate conservative treatment with clinical signs of instability on examination.