This article is more than 5 years old. Information may no longer be current.
Tibial tubercle transfer with MPFL reconstruction addresses patellar instability
Click Here to Manage Email Alerts
Recurrent patellar instability continues to be a challenge for orthopedic surgeons. Although first-time dislocations are often successfully treated with nonoperative management, surgical intervention is indicated for recurrent dislocations. Ideology of patellofemoral instability is multifactorial, including structural and anatomic factors. Limb alignment, soft-tissue integrity and osseous anatomy need to be carefully considered in treating this problem.
Physical examination is helpful in identifying soft tissue integrity by assessing the lateral mobility of the patella and osseous anatomy by evaluating patellar tracking. Radiographs are used to evaluate for patellar tilt, subluxation and trochlear dysplasia. MRI is used to evaluate integrity of medial patellofemoral ligament (MPFL), chondral injury, presence of bony lesions or loose bodies, tibial tubercle-trochlear groove distance or the tibial tubercle to posterior cruciate ligament distance, as well as the patellotrochlear engagement index. In patients with normal bony anatomy, MPFL reconstruction has been shown to be successful. However, distal realignment procedures are often indicated in patients with increased tibial tubercle-trochlear groove (TT-TG) distance and/or patella alta.
This Surgical Technique article describes the surgical considerations and our preferred surgical technique for a tibial tubercle transfer with MPFL reconstruction.
Surgical considerations
In patients with recurrent patellar instability, anteriorization and medialization of the tibial tubercle are performed in the setting of normal patellar height to normalize the TT-TG and potentially unload the patella. In the case of a significant patella alta (Caton-Deschamps ratio greater than 1.3), distalization can be performed using the same technique. The Caton-Deschamps ratio is helpful as it will change with the tibial tubercle osteotomy. The actual measured difference between the proximal vs. the distal arm will provide the amount of distalization (in millimeters) needed to obtain a Caton-Deschamps ratio of 1.
Generally, a TT-TG distance of greater than 20 mm is considered to be an indication for medialization of the tibial tubercle (back to a normal mean value of 10 mm to 14 mm).
Surgical techniques
Images: Lattermann C
Preoperative femoral/static nerve block is performed. The patient is placed supine on a standard OR table and is induced with general anesthesia. The patient’s patellar laxity and tracking are evaluated under anesthesia before a padded, non-sterile tourniquet is placed on the affected thigh. The leg can be positioned flat or in an arthroscopic leg holder for this surgery.
For arthroscopy, we initially perform an arthroscopic evaluation of the knee joint to evaluate the stability of the patella under direct vision (Figure 1). We identify potential loose bodies and chondral damage to the trochlea, the patella or the lateral condyle.
To perform a tibial tubercle transfer (modified Fulkerson osteotomy), a single midline incision is made from the inferior pole of the patella down to the tubercle until the patella tendon is exposed. The patella tendon is then carefully dissected medially and laterally from its insertion into the tibial tubercle to about 1 cm proximal using an electrocautery knife (Bovie Medical). An army navy retractor is utilized to visualize the patella tendon insertion posterior to the actual tendon into the proximal tibia. Using a 0.25-inch osteotome, a transverse cut is made across the attachment site in the sagittal plane. The edges of this cut are marked in a proximal to distal fashion with a 0.5-inch osteotome. These cuts serve as stress risers to prevent a breakout into the joint when the tubercle osteotomy is completed. The tibialis anterior fascia is incised with the electrocautery knife, and the tibialis muscle is carefully pushed away from the tibia in a blunt fashion using the large periosteal elevator.
A retractor (Tracker AMZ Guide System, DePuy Synthes) (Figure 2) is positioned behind the tibia to retract the anterior tibialis. The cutting block guide (Tracker AMZ Guide System, DePuy Synthes) is then positioned such that the proximal end is fixed to the medial corner, which is defined by the initial horizontal osteotome cut and the medial most extent of the patella tendon insertion. A 2-mm or 2.5-mm drill will fit into the uppermost slot and will serve as a fixation of the cutting block once the inclination angle has been determined (Figure 3). The inclination angle is important, as it defines the amount of anteriorization vs. medialization (Figure 4). More vertical positioning will lead to more anteriorization, while more horizontal positioning will lead to more medialization of the tibial tubercle.
The left side of the image is proximal, and the right side is distal. The skin marking for the inferior pole of the patella is seen just proximal to the incision. The gray arrow indicates the location for the superior transverse cut of the tibial tubercle on the sagittal plane.
The image shows the leg from the lateral side. The tibialis anterior muscle is retracted posteriorly with the retractor, which is placed behind the tibia as seen in the image.
Once the AMZ Guide is properly positioned, the distal end of the guide is manually stabilized. A drill can be positioned to do this. However, the length of the guide may result in a cut that is too long in smaller individuals, pre-disposing the tibia for a stress fracture in the future. The cut is made from the medial side through the medial cortex and through the lateral cortex onto the AMZ retractor. The osteotomy is completed using a wide osteotome that is proximally advanced up to the height of the transverse cut.
If done correctly, the tubercle piece should have a triangular shape and should be about 6 cm to 8 cm long. One more cut is critical to finish the osteotomy at this stage. A posterior directed cut has to be performed starting at the intersection of the transverse cut and the lateral patellar tendon, where the initial 0.5-inch osteotome score was positioned; this cut will free the tibial tubercle fragment. Next, the tubercle is elevated; the fat pad is released; and the tubercle is wrapped in a moist gauze.
At this time, the gracilis tendon is identified and a sharp incision is made along the tendon and distally at its insertion to creating upside down L-shaped leaflet of sartorial fascia. The gracilis tendon is dissected off the posterior side of the fascia and placed in an Allis clamp. The end of the graft is whipstitched at this time and traction is applied to release adhesions using primarily blunt dissection. Using a tendon stripper, the tendon is carefully harvested.
Lateral retinacular lengthening is performed by sharply dissecting on the lateral aspect of the patella two layers of the retinaculum. Initially, the outer layer of the retinaculum is incised and the two layers are separated. The deep layer is incised posteriorly just above the capsule to allow for layered Z-lengthening at completion of the procedure. At this point, there is complete access to the patellofemoral joint and any additional intra-articular work can be done to address any chondral or bony lesions.
The tibial tubercle must be fixed before MPFL is reconstructed. The tubercle is placed in its desired position; this is measured by ruler to correct the calculated amount of medialization and distalization based on preoperative measurements on the Caton-Deschamps and TT-TG evaluation. The tubercle is secured in place with a K-wire (Arthrex)(Figure 5).
A large fragment lag screw technique is used to fix the tubercle to the proximal tibia. Typically, we will use two partially threaded cancellous 4.5-mm screws to secure the tubercle. We have abandoned the use of cortical screws for this technique due to recurrent issues with purchase in the posterior tibial cortex. We also use countersink to minimize screw prominence anteriorly. Cancellous bone chips can be used to fill the bone defect around the tubercle after transfer.
MPFL reconstruction
The medial aspect of the proximal patella is exposed (through the tubercle incision or through a curved 3-cm incision). The electrocautery knife is used to identify and mark the 1 o’clock and 3 o’clock positions for the right knee or 9 o’clock and 11 o’clock positions for the left knee. The electrocautery knife is then used to elevate the periosteum between those two marks, which are anteriorly stripped. A small rongeur is used to create a shallow trough in the horizontal plane connecting the 1 o’clock and 3 o’clock positions; this serves as a bony trough for better attachment of the MPFL graft. A 2-mm drill is used to create tunnels in medial to lateral direction at 1 o’clock and 3 o’clock positions. Using the drill, the drill hole is widened through excentric circular movements upon exiting the drill hole in order to create a socket for the tendon graft. A suture passer (Hewson Suture Retriever, Smith & Nephew) is passed through the patellar tunnels, and a counter incision is made on the lateral aspect of the patella to retrieve the sutures. Two 0-vicryl sutures (Ethicon) are fed through the patellar tunnels as pull sutures.
The leg is brought into 90° of flexion, while mini C-arm is brought in and a perfect lateral image of the distal femur is obtained. Using the technique called ‘Schöttle’s point’ described by Philip Schöttle, MD, and his colleagues, the intersection of the posterior femoral line, Blumensaats line and the physeal scar is identified with a beath pin. A 2-inch skin incision is carried through the skin and soft tissues down to the adductor fascia. The pin is again positioned at Schöttle’s point under fluoroscopic control.
A digital palpation of the adductor tubercle can be performed to verify the pin position. The beath pin is passed through the femur and recovered laterally through the skin. A 7-mm Acorn ACL reamer (Arthrex) is utilized to create a socket by drilling across the distal femur up to the lateral cortex. Then a flexible nitinol pin for guidance of the bioabsorbable screw is placed.
It is important to do this step at this time because once the beath pin has been pulled through the distal femur, it is difficult to find the drill hole for the flexible guide pin.
Using the 0-vicryl passing sutures in the patellar tunnels, the two reinforced suture ends of the graft are passed through each patella hole and the graft is tightly docked into the medial patella. The sutures are then tied down directly on to lateral patella with two strands of suture tied to the other two strands (approximately four knots), followed by separately tying each strand to the other (approximately three knots). Three of the four strands are cut, and the last strand is used to bury the knot in the lateral soft tissues with a free needle. The soft tissue around the knot is closed over the knot with 0-vicryl to prevent irritation.
Next, a tonsil is passed and a large #5 reinforced suture is passed from the medial patellar incision under fascia in layer two and three to the femoral incision using a tonsil with the looped end going around the looped graft; this is used to shuttle the graft. The ends of the FiberWire suture (Arthrex) are then passed through the beath pin and pulled through the femoral tunnel. Sutures are pulled to fully dock the looped end of the graft into the femoral tunnel. At this time, the medial side will be over-constrained with medial shift of the patella. The knee is then taken through full range of motion (ROM) into deep flexion until the patella is reduced and centralized.
We consider this maneuver important to set the length of the MPFL for the entire ROM cycle; this way, we assure no over-constraint of the kneecap in flexion. The patella is then stabilized in the trochlea with the knee bent to 30° of flexion, and the pull suture for the tendon graft is held tight laterally.
No ‘tensioning’ of the graft is performed. Fixation of the femoral side is achieved using a bioabsorbable screw. While tightening the screw, it is important to stabilize the patella and slightly pull laterally, as tightening the screw may pull the tendon graft further into the femur, thus overtightening the MPFL graft.
After the MPFL is reconstructed, the lateral retinacular lengthening can be completed by repairing the anterior superficial and deep posterior layers of the retinaculum, which were previously dissected back together with 0-vicryl. The tibialis anterior fascia is then re-approximated using a 0-vicryl suture, and the skin is closed in layers with two 0-vicryl and four 0-monocryl sutures (Ethicon). We utilize postoperative knee braces in order to keep the extremity in extension and for general safety precautions.
Postoperative rehabilitation
Rehabilitation is focused on recovery. We position our patients in a postoperative brace (TROM Advance, DJO Global), which is locked in extension for 1 week.
Physical therapy will predominantly work on reduction of swelling. Physical therapy is started at the first postoperative visit with isometric quad strengthening in extension, e-stim and patellar mobility without lateral glides. We increase the permitted ROM by 30° each week, starting at first postoperative visit to allow full motion at 4 weeks. Progressive quadriceps strengthening is added at around 4 weeks to 6 weeks, and straight-leg raises can be trained with an unlocked brace if there is no patellar lag. The brace is kept locked in extension for ambulation until the patient is able to perform a full straight-leg raise without lag.
Weight-bearing is limited to toe touch with crutches for the first 4 weeks postoperatively and is advanced to full weight-bearing by 6 weeks. The brace is changed to a lateral stabilizer brace at 6 weeks, and all brace use can be discontinued at 8 weeks postoperatively. Closed-chain strengthening and use of the stationary bike/elliptical are initiated at 6 weeks. Patients are advanced to running straight at 12 weeks, and functional drills for athletes are started at 4 months to 6 months.
- References:
- Arendt EA, et al. Knee Surg Sports Traumatol Arthrosc. 2013;doi:10.1007/s00167-012-2274-1.
- Biedert R. 2004. Lateral patellar hypercompression, tilt and mild lateral subluxation. Chichester, England: John Wiley & Sons.
- Fulkerson JP. Clin Orhop Relat R. 1983; doi:10.1097/00003086-198307000-00027.
- Merican AM, et al. J Bone Joint Surg Br. 2008;doi:10.1302/0301-620X.90B4.20085.
- Post WR. J Am Acad Orthop Surg. 2005;13(8):534-543.
- Schöttle P, et al. Arch Orthop Trauma Surg. 2009;doi:10.1007/s00402-008-0712-9.
- For more information:
- Berkay Unal, MD, is a fellow at the Department of Orthopaedic Surgery and Sports Medicine, University of Kentucky. He can be reached at 740 S. Limestone, Lexington, KY 40536; email: berkay.unal@uky.edu.
- Christian Lattermann, MD, is a professor, the vice chair for clinical research and the director at the University of Kentucky Center for Cartilage Repair and Restoration and medical co-director at the Sports Medicine Research Institute. He can be reached at the University of Kentucky, 740 S. Limestone, Lexington, KY 40536; email: clatt2@uky.edu.
Disclosures: Unal and Lattermann report no relevant financial disclosures.