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Bone-patella tendon-bone autograft harvest calls for attention to detail
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The patella tendon is an ideal graft for knee ligament reconstruction, especially for ACL reconstruction. The ability to harvest bone attachments on both ends of this graft allows for interference screw fixation within a bone tunnel, as well as bone-to-bone healing within that tunnel.
Brett D. Owens
However, this ideal graft does have its downsides, which are primarily related to the donor site morbidity and risk of subsequent anterior knee pain. In addition, surgeons who do not perform a high volume of ACL reconstructions may not be as comfortable with this graft harvest and its potential pitfalls and complications. In this article, I share my approach to bone-patella tendon-bone autograft harvest.
Harvest surgical technique
The knee is draped free over a tourniquet, which is not routinely inflated, but is available. Adequate hemostasis is critical for visualization; however, this is usually achievable with electrocautery and careful surgical technique. The surface anatomy is marked, and the incision is planned (Figure 1). A midline incision is made over the patella tendon, with visualization over the bone plugs usually possible with retraction, especially in the superior direction. Alternatively, a medialized incision can be used and extended distally to incorporate the tibial tunnel incision. The approach is performed with the knee in extension as this takes the tension off the tendon and allows for easy retraction of the patella. With the patient’s foot stabilized on the surgeon’s thigh, flexion can easily be achieved when necessary. Sharp and blunt dissection is carried down to the paratenon. Blunt finger dissection can be facilitated with the use of a sponge draped over the finger. The paratenon is incised longitudinally along the length of the incision and dissected free of the underlying tendon, facilitating a layered closure. Again, blunt finger dissection can be used to mobilize the paratenon in an expeditious manner while minimizing the risk of tearing of the paratenon (Figure 2). A Kelly clamp is passed posterior to the tendon and serves as a retractor for the remainder of the harvest. Sliding the clamp proximally and distally can help free the tendon from posterior attachments. The tendon width is measured, and the central third is marked (Figure 3). This is typically a 10-mm graft for a 30-mm tendon or 9-mm graft for a 27-mm tendon. The tendon incision can be made with a double-bladed scalpel, although a single-blade scalpel works as well. Often the tendon split can be propagated bluntly with a freer elevator to avoid transecting tendon fibers.
Figure 1. The surface anatomy is marked and an incision is planned over the patella tendon. Also marked is the position for the tibial tunnel, three finger breadths below the joint line and in the middle of the tibia.
Figure 2. The paratenon is split along the length of the tendon and carefully dissected from the underlying patella tendon.
Images: Owens BD
We begin our bone plug harvesting on the patellar side, using a patella retractor which both retracts the skin and delivers the patella into the wound. The proximal tendon split is carried up to the distal pole of the patella, and the bone is marked with the Bovie electrocautery. Accurate marking of the tendon-bone interface is critical, as the tendon graft fibers should be confluent with the tendon insertion on the bone plugs. An appropriate width bone plug is then marked, typically with a 10-mm width. The marking of the bone plug length can be facilitated with an understanding of the electrocautery tip length (typically 25 mm), with the goal of a 20-mm plug (Figure 4).
Figure 3. A Kelly clamp is placed behind the patella tendon and the tendon width is measured and the central third marked.
Figure 4. The Bovie electrocautery tip is used to estimate the length of the patella bone plug and used to carefully plan the bone cuts.
The oscillating saw is used to score the marked bone plug with particular attention paid to the corners for completeness while avoiding extending the cuts beyond the plug, which can become a stress riser. A 3/8-inch curved osteotome can be used to complete the harvest and deliver the plug, but excessive use of a mallet should be avoided to limit trauma to the underlying patella articular cartilage. Once free, the plug is pushed back into its donor site and attention is turned to the tibial bone plug.
If the assistant and surgeon change positions so that the surgeon works from a proximal position, the surgeon can better visualize the tibial harvest and minimize the length of incision that is necessary. The tendon splits are carried distally into the tibial periosteum using electrocautery. Care should be taken to preserve a 10-mm wide footprint of tendon insertion on the bone plug. The length on this side is less critical from the perspective of donor site morbidity; therefore, a 30-mm plug can easily be harvested. The tibial plug is demarcated and harvested using the oscillating saw and osteotome in a similar fashion to the patella plug harvest. When the tibial plug is freed, it is again kept in its donor site and the surgeon resumes a position at the foot of the patient.
The graft is secured in one hand, and with tension on the graft, a Mayo-curved scissors is used to dissect the fat pad from the posterior aspect of the graft. The graft is then securely carried to the back table for preparation. Personally carrying the graft to the back table minimizes the risk of graft being dropped and contaminated.
Graft preparation and insertion
On the back table, the graft is evaluated for its overall length, the width and length of each plug, and the tendon length between the plugs. The tendon length should correlate with the preoperative measure from the sagittal MRI.
Tendons longer than 55 mm present concerns for graft-tunnel mismatch. This can be addressed in a few ways to include recessing the plug in the femoral socket, as well as twisting the graft. If significant mismatch still exists, a soft tissue screw can be placed alongside the tendon graft in the tibial tunnel, and the tibial bone plug can be secured with a staple into a cortical trough made with a burr. If significant mismatch is identified preoperatively (>55 mm tendon length), it can be addressed on the femoral side with outside-in drilling of the femoral tunnel and interference screw fixation on the lateral femoral cortex.
The graft bone plugs are debrided to fit into a 10-mm cylindrical guide with the cancellous bone removed primarily. Chamfer cuts on the end of the femoral plug can help facilitate passage. Drill holes are placed in the bone plugs in orthogonal planes or divergent trajectories to minimize the risk of bone plug breakage. If utilizing anteromedial portal drilling, the bone plug being placed into the femoral socket should be trimmed to a maximum length of 22 mm. This helps facilitate turning the graft in the notch (Figures 5 and 6).
Figure 5. The patella bone plug length is trimmed to 20 mm to facilitate insertion into the femoral socket.
Figure 6. The 10 x20-mm bone plug is turned in the notch to facilitate passage into the independently drilled femoral socket, which was created in this case via an anteromedial portal.
While the graft is being prepared, the diagnostic arthroscopy is performed and any meniscal work is completed. The midline patella incision can be used to create the lateral and medial arthroscopy portals and thereby minimize the incisions used (Figure 7). During creation of the tibial tunnel, a guide pin is placed into the tibial footprint of the ACL. The tibial cortex is breached with a solid 10-mm cylindrical reamer followed by the harvesting of a bone graft plug using a cannulated coring cylinder (8 mm) performed by hand. After bone graft harvest, the tunnel is completed with the 10-mm reamer.
Figure 7. The arthroscopy is performed via medial and lateral portals placed through the harvest incision.
This usually results in a quality plug of cancellous bone to help backfill the harvest sites. A coring reamer used on power can often stray from the guide pin and is not accurate enough for tibial tunnel creation.
Backfill and closure
Once the graft is secured, the procedure is not completed. Careful attention to the graft donor sites is critical to mitigate complications and help the athlete return to competition.
Figure 8. The immediate postoperative lateral
radiograph shows complete backfill of harvest
sites on the patella and tibia.
After copious wound irrigation, the bone graft available is assessed and packed into the patella site first. The paratenon is closed over this backfill using a running stitch pattern with absorbable suture. The tendon proper is not closed in a side-to-side fashion, but one side of the tendon can be used to assist closure if the paratenon is of poor quality. The tibial harvest site is then grafted with the remaining bone and the closure completed. Some surgeons have placed platelet-rich plasma into the tendon defect, yet the benefit of this adjunctive treatment has not been defined.
The skin is then closed in layers. Quality bone grafting can result in radiographs that show complete fill of the donor deficits (Figure 8) and may result in improved outcomes, as many patients complain of pain when kneeling directly on the tibial tubercle harvest site.
In summary, bone-patella tendon-bone autografts are ideal grafts for ACL reconstruction and are well tolerated in young athletes. Attention to detail during the graft harvest as well as the donor site closure can help the athlete recover from this insult to their extensor mechanism.
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Disclosure: The views and opinions expressed in this manuscript are those of the author and do not reflect the official policy of the Department of the Army, the Department of Defense or the U.S. Government. Owens is a paid consultant for Musculoskeletal Transplant Foundation and Mitek Sports Medicine.