Patellar Bone-Grafting for Severe Patellar Bone Loss During Revision Total Knee Arthroplasty.

Background Treatment of severe patellar bone loss during revision total knee arthroplasty (TKA) is difficult. Patellar bone-grafting is a simple procedure that can improve patient outcomes following revision TKA. Description The patient is prepared and draped in the usual sterile fashion. The previous longitudinal knee incision is utilized for exposure. Scar tissue is excised from the medial gutter. However, tissue in the lateral gutter is largely maintained. An assessment of the surrounding quadriceps and patellar scar tissue ensues. This tissue can be utilized to create an envelope for holding the bone graft in place. If insufficient tissue is present, fascia from the iliotibial band or vastus medialis, allograft fascia, or synthetics can be used.A careful assessment of component fixation and rotation is critical to the success of patellar bone-grafting. Component revision for aseptic loosening or malrotation should be performed in the usual fashion. During component revision, it is recommended to preserve any additional bone as autograft for the patellar bone-grafting procedure. Common sites of autograft harvest include the femoral box cut and proximal tibial resection.The patella is then addressed by carefully removing the previous implant to avoid additional bone loss. This step is performed with a combination of an oscillating saw, osteotomes, and high-speed burr. The retropatellar bone is then prepared by debriding excess soft tissue, cysts, or cement. A high-speed burr is then utilized to produce a punctate bleeding surface for bone-graft incorporation.The harvested tissue is closed around the perimeter of the patella with use of interrupted nonabsorbable sutures, leaving a window to pack in the bone graft. The bone graft (allograft and autograft) is morselized and place through the window.The optimal patellar thickness is variable. After packing the bone graft through the soft-tissue window, the thickness is measured with a caliper. It is recommended to acquire a thickness of >20 mm because bone-graft resorption and remodeling occur with knee range of motion. The remaining soft-tissue window is closed with use of nonabsorbable sutures. The knee is cycled through a range of motion to ensure optimal patellofemoral tracking. If necessary, a lateral release or medial soft-tissue advancement can be performed to ensure patellofemoral tracking is adequate. Finally, the wound is irrigated and closed in layers. Alternatives Nonsurgical:Patellar knee braceHinged knee braceSurgical:Gull-wing osteotomyPatellar resurfacing with biconvex patellaBulk allograft reconstructionPartial or complete patellectomyPatelloplastyInterpositional arthroplastyTantalum metal-backed reconstruction. Rationale There is a myriad of surgical options for severe patellar bone loss following TKA. Patellar bone-grafting is simple, reproducible, and relatively cost-effective1,2, and avoids the need for the amount of bone for reconstruction that may be required for metal-backed or biconvex patellar implants3,4. The procedure allows for the restoration of the quadriceps lever arm, which may not be restored with other techniques, such as gull-wing osteotomy or patellectomy5. Patellar bone-grafting avoids the cost and risks of disease transmission associated with allograft reconstruction6. Finally, the procedure provides excellent long-term survivorship and patient-reported outcomes. Expected outcomes Following this procedure, patients should experience a reduction in knee pain and improved patient-reported outcomes2,6, with a prior study showing that the percentage of patients reporting anterior knee pain decreased from 51% to 27% following patellar bone-grafting. Patients also demonstrated an improvement in knee range of motion, with a mean increase in knee flexion of 7o and knee extension of 2o1. Complications related to this procedure are minimal. Bone stock restoration can be utilized for patellar resurfacing in the future1. Radiographically, patellar bone resorption, loss of patellar height, and patellar remodeling do occur; however, despite these radiographic changes, Knee Society scores increased from 50 to 85 at the time of the latest follow-up. Important tips Careful preoperative physical examination should document range of motion, areas of pain, and patellofemoral tracking and/or instabilityBe prepared to revise the femoral and/or tibial components if malrotated in order to optimize patellofemoral trackingRetain any autogenous bone harvested during component revision to use as patellar bone graftEnsure that allograft bone is available to ensure sufficient restoration of patellar thicknessConsider having allograft tissue available in the event that scar tissue in situ is not adequate to create an envelope for packing the bone graftA bleeding retropatellar surface prepared with a high-speed burr will increase the chance of bone incorporationA watertight closure of the soft-tissue envelope is critical to avoid loss of bone graft during knee range of motion.