Date Published: September 26, 2011
Publisher: SAGE-Hindawi Access to Research
Author(s): Raul A. Kuchinad, Shawn Garbedian, Benedict A. Rogers, David Backstein, Oleg Safir, Allan E. Gross.
Bone loss around the knee in the setting of total knee arthroplasty remains a difficult and challenging problem for orthopaedic surgeons. There are a number of options for dealing with smaller and contained bone loss; however, massive segmental bone loss has fewer options. Small, contained defects can be treated with cement, morselized autograft/allograft or metal augments. Segmental bone loss cannot be dealt with through simple addition of cement, morselized autograft/allograft, or metal augments. For younger or higher demand patients, the use of allograft is a good option as it provides a durable construct with high rates of union while restoring bone stock for future revisions. Older patients, or those who are low demand, may be better candidates for a tumour prosthesis, which provides immediate ability to weight bear and mobilize.
Dealing with bone loss when performing primary or revision total knee arthroplasty is a challenge for the arthroplasty surgeon. Previous infections, tumour, and trauma can all result in bone loss that makes a standard primary total knee arthroplasty impossible without restoration of bone stock. More commonly, bone loss in revision knee arthroplasty is a frequent problem and may occur for any of the aforementioned reasons, osteolysis, periprosthetic fracture, or iatrogenically when components are being removed from host bone.
There is no universally accepted classification that is currently used for describing bone loss in knee arthroplasty. Engh developed the Anderson Orthopaedic Research Institute (AORI) classification system that helps to guide treatment for both femoral and tibial sides in revision knee arthroplasty (see Table 1) .
Allograft harvesting should be done according to the criteria of the American Association of Tissue Banks, in sterile conditions and in our institution followed by irradiating the tissue at 25,000 Gy and storage at −70°C . Although some believe that donor allograft does not have to be matched to the recipient’s anatomy, others argue that modifying the allograft weakens it. If the allograft is size matched, application of the graft becomes easier to use in the patient and maintains its inherent strength. Also, allografts that are oversized may make the soft-tissue closure difficult or impossible to perform which is a serious intraoperative complication. To ensure this does not happen, we recommend taking preoperative calibrated radiographs of the allograft and comparing this with the patient’s radiographs .
The primary indications for using structural allografts in the setting of arthroplasty are (a) large uncontained defects that are outside the range of metal augments or thicker polyethylene inserts (see Figures 1 and 2), (b) patients that are active and require bone-stock restoration for potential future operations, and (c) patients who are physically well enough to tolerate both the surgical procedure and rehabilitation required for successful outcomes. A relative contraindication is a patient actively smoking, and cessation programs must be implemented prior to surgery. Lastly, presence of active infection is an absolute contraindication for allograft in the arthroplasty patient.
In the setting of previous infection or posttraumatic defects, active infection must be ruled out. C-reactive Protein, erythrocyte sedimentation rate, and possible knee aspirate should be performed prior to planning any knee arthroplasty procedure especially with use of allografts. Once infection is ruled out, careful planning should include 4 foot standing radiographs of both limbs, standard AP, lateral, and skyline views and, if required, a CT scan. CT scanning can help with determination of whether the defect is contained or uncontained and overall dimensions. As always, these investigations must be combined with a thorough physical exam of the patient, which includes limb alignment, ligamentous stability, and a neurovascular exam.
Old operative reports detailing prior surgical approaches should be obtained to help the surgeon decide on the optimal exposure. Ideally, use of a midline incision and a parapatellar arthrotomy (medial or lateral) should be reused in the revision surgery to minimize the remaining blood supply to the skin and patella.
Small contained defects less than 10 mm can be treated with morselized autograft, allograft, or cement alone. Uncontained defects that are less than 10–20 mm in size can be treated with metal augments alone; however, larger defects can be dealt with structural allograft or tumour implants . Bone loss of the proximal tibia that involves the entire surface can be treated with metal augments and a thicker polyethylene insert, but the upper limit for this is 45 mm. An alternative option is structural allograft or tumour prosthesis.
Massive segmental bone loss of either the femur or tibia cannot be treated with cement, augments, or segmental allograft bone alone and require an allograft-prosthetic component (APC) or tumour prosthesis. These defects are uncontained and are frequently circumferential and involve >25 mm of the femur or >45 mm of the tibia.
The allograft-prosthetic composite of the tibia is fashioned to size based on careful measurements of the host tibia after a thorough debridement is performed. As always, making the allograft larger and longer than may actually be required is good practice as it is always easier to trim the graft “down to size” if needed. This saves time and avoids unnecessary waste of allograft. As in any stemmed implant, the host canal is reamed to secure a press-fit stem that should bypass the allograft-host junction by two cortical diameters or by approximately 5 cm. The proximal extent of the allograft should restore the normal biomechanics of the knee and that ultimately means the joint line of the implant should be 10–15 mm proximal to the tip of the fibular head. Again, use of the step or oblique cut is utilized to optimize the stability of the implant. Rotational position is a challenge to determine; however, use of anatomical landmarks such as the tibial tubercle, patellar tendon, and patellar tracking all assist the surgeon in placing the allograft in the correct rotation. This rotational and joint-line position should be judged with the trial implants in place. The knee should be taken through a range of motion to examine the patellar height and tracking. Minor adjustments can be made easily at this stage to improve the knee biomechanics. When the surgeon is satisfied with the rotation and height, the position should be marked with cautery and a marking pen. This assists in final implantation of the APC into the proper overall orientation.
The epicondylar attachments of the collaterals, which were preserved during exposure, are critical in the securing of the femoral APC. As in the tibia, the femoral canals are reamed to securely fit a stemmed implant with proximal fixation into the host bone of two cortical diameters or a minimum of 5 cm. On the back table, the femoral APC is prepared with the revision cutting guides to make the appropriate bone resections (see Figure 3). The epicondylar attachments of the collaterals are secured to the allograft through transosseous drill-hole tunnels where the collateral ligaments would be in a native distal femur. Sutures are passed through these tunnels and left long to attach the host collaterals once the APC is implanted.
During primary or revision arthroplasty the extensor mechanism can be deficient secondary to tubercle avulsion, tendon rupture, proximal tibial bone loss, or erosion of the extensor mechanism from infection. During revision, arthroplasty scarring of the quadriceps and patellar tendon makes the extensor mechanism particularly vulnerable to disruption.
Closure of the wound may be challenging, and the most common reason for this is oversized allograft, followed by oversized components. To avoid this problem, careful implant and allograft selection is critical. Tibial tubercle osteotomy is attached with large fragment partially threaded cancellous screws or with transosseous wiring. Quadriceps tendon turn-down or snips are repaired with heavy suture. Closure of the parapatellar arthrotomy is done with heavy suture done in a continuous manner with reinforced interrupted sutures. Deep drains are placed at the preference of the surgeon and subcutaneous and skin layers are closed in the usual fashion. Anticipated wound closure problems should be discussed prior to surgery with your plastics colleagues. If soft-tissue coverage is a problem, rotational flaps and skin-grafting may be necessary .
Range of motion is a critical component of recovery, and these should be started as soon as possible provided the wound coverage is adequate and there are no extensor mechanism issues. If a tibial tubercle osteotomy or quadriceps turndown is performed, we restrict active extension for 6–8 weeks. Restrictions on weightbearing are maintained for 8 weeks followed by progressive increases to full weightbearing once graft incorporation is seen on sequential radiographs. This may take 3–6 months depending on the reconstruction and biology of the patient.
As with all complex reconstructions, preoperative planning is critical in ensuring no untoward intraoperative surprises. We strongly believe that deviating from a carefully thought-out preoperative plan may result in poor outcomes. Critical steps involve allograft and implant sizing and dealing with anticipated wound complications early and aggressively. Furthermore, optimizing the patient’s perioperative health status is crucial, and this must include smoking abstinence.
The use of segmental and structural allografts has been used in both contained and uncontained defects around the knee in arthroplasty for over two decades. The primary data for this comes in the setting of revision knee arthroplasty and has encouraging results. In one of the earliest papers, Stockley et al. reported 20 knees that had undergone a combination of structural allograft and morselized allograft with 85% survivorship at 4.2 years . There were 2 graft fractures and 3 infections in their series. The lowest reported survivorship is that from Ghazavi et al. with only 67% survivorship at 5 years in their 30 patients . However, when looking at the majority of the literature, most authors report 80–93% survivorship of their constructs at 5 years. The survivorship numbers drop off at 10 years with Clatworthy et al. showing a drop of 92% at 5 year to 79% at 10 years . Reference  had 46 patients at 10 years with 91% survivorship for femoral head allograft in tibial defects.
Dealing with bone loss is a significant challenge to arthroplasty surgeons. We believe that structural allograft is a viable method for dealing with this problem with the added benefit of restoring bone stock. These complex procedures should be performed by surgeons with expertise in revision arthroplasty and with access to a dedicated bone bank. Allograft reconstruction is not indicated in the low demand or elderly patients who would benefit from implantation of an endoprosthesis, which allows rapid mobilization and recovery.