KNEE Structured oralexamination question6: Anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) reconstruction
EXAMINER: These images belong to a 26-year-old rugby player. He gives a history of falling awkwardly on to his left knee after a heavy tackle. What can you see? (Figure 3.6.)
CANDIDATE: These are plain radiographs and MRI of the right knee. The most obvious abnormality is cortical disruption at the site of PCL insertion with displaced avulsed fragment. The lateral radiograph shows this is a large fragment which is displaced into the joint.
EXAMINER: How would you treat this patient?
CANDIDATE: I would offer this patient reattachment of the PCL avulsion through open procedure.
EXAMINER: What approach would you use?
CANDIDATE Posterior approach.
EXAMINER: Tell me about posterior approach to the knee.
CANDIDATE: The indications include removal of popliteal cysts and neoplasms, posterior synovectomy, open reduction and internal fixation of posterior tibial plateau shear fractures, fixation of bone avulsions associated with a posterior cruciate ligament (PCL) injury, repair of posterior vascular injuries, and more recently, posterior inlay PCL reconstructions. The patient is usually positioned prone with tourniquet high up in the thigh. The lazy S-shaped incision is made starting posterolaterally along the border of biceps femoris tendon crossing the popliteal fossa and ending posteromedially at the posterior border of semitendinosus tendon. The deep fascia is incised in the midline. The small saphenous nerve is identified with accompanying sural nerve that must be preserved. The sural nerve is traced proximally where it pierces deep fascia from the tibial nerve trunk. At the apex of the fossa, the common peroneal nerve separates from tibial nerve. The tibial nerve lies posterior to the popliteal vein which in turn is superficial to popliteal artery. Popliteal vessels are displaced laterally and this usually requires ligation of middle geniculate and superior medial geniculate vessels. The medial head of gastrocnemius is identified, traced proximally and can be detached from its origin then retracted towards midline to expose the medial joint capsule. Similarly the lateral head of gastrocnemius can be detached to expose the posterolateral corner of the joint. The main structures at risk are the popliteal vessels, small saphenous vein and common peroneal nerve and tibial nerve.
EXAMINER: Have you been involved in any arthroscopic PCL reconstruction?
CANDIDATE: Yes (despite never having seen one!)
EXAMINER: What is the optimum tunnel placement?
CANDIDATE: The tunnel placement in PCL reconstruction depends on whether it is single-bundle or double-bundle reconstruction ...
EXAMINER: Tell me about the one you have seen.
CANDIDATE: The optimum placement of PCL tunnel is controversial. The literature shows that the femoral tunnel for posterolateral bundle reconstruction should be placed at
1.30 o’clock ...
EXAMINER: Are you sure? (Realizing that the candidate is bluffing.)
CANDIDATE: To be honest I have not seen many of these but I will check on it.
EXAMINER: Let’s move on. Now tell me about the optimum tunnel placement for single bundle ACL reconstruction.
CANDIDATE: The principles of ACL reconstruction are placement of tunnel anatomically and isometrically, using biologically active grafts which are adequately tensioned to allow early rehabilitation. In single-bundle reconstruction, the aim is to place tunnel at the footprint of the posterolateral bundle of ACL. The anteromedial bundle is thought to be the most isometric but most surgeons feel that it’s important to replace the posterolateral bundle. For the femoral tunnel the isometric point lies at about 10 to 10.30 o’clock for right knee and 1.30 to 2 for left knee. The most common mistake is to place femoral tunnel too anterior or ‘resident’s ridge’. This restricts flexion of the knee and may result in elongation of graft. Similarly, too posterior tunnel placement results in excessive tightening of graft when knee is extended. It’s been shown that abnormally narrow intercondylar notch correlates directly with increased incidence of ACL tears. Careful assessment of notch should be done prior to graft insertion using a pin to ensure no impingement on lateral femoral condyle. The presence of impingement with correct placement of tunnels necessitates notchplasty of the anterior portion of lateral femoral condyle.
EXAMINER: Which graft would you use and why?
CANDIDATE: I would use a hamstring four-strand autograft. The two main biological autografts used in ACL reconstruction are hamstring and bone patella tendon bone (BPTB) graft. The BPTB graft has the advantage of being easy to harvest, rigid fixation and faster integration as it uses bone to bone healing. However, it has donor site morbidity which includes anterior knee pain in 30–50%, patellar tendonitis 3–5%, patellar fracture and patella baja. The hamstring graft on the other hand has less donor site morbidity, can be harvested from a small incision and can be passed relatively easily. However it has slow healing because of tendon to bone incorporation which takes 8 to 12 weeks. It can also result in hamstring weakness and saphenous nerve injury. There are several studies comparing outcome of BPTB versus hamstring graft. Most studies show arthroscopic reconstruction with either graft results in similar functional outcome but increased morbidity in BPTB in form of early OA and increased knee laxity with radiographic femoral tunnel wide in hamstring graft.
Feller JA, Webster KE. A randomized comparison of patellar tendon and hamstring tendon anterior cruciate ligament reconstruction. Am J Sports Med 2003;31:564–573.
Howell SM, Taylor MA. Failure of reconstruction of the anterior cruciate ligament due to impingement by the intercondylar roof. J Bone Joint Surg Am 1993;75-A:1044.
Pinczewski LA, Deehan DJ, Salmon LJ, Russell VJ, Clingeleffer A. A five-year comparison of patellar tendon versus four-strand hamstring tendon autograft for arthroscopic reconstruction of the anterior cruciate ligament. Am J Sports Med 2002;30:523–536.
Debrief: With a thorough understanding of ACL reconstruction, the candidate has recovered from a bad start of this viva. Candidates should be honest and be prepared to say they have not seen some operations.
