Published Works: Special Considerations for Growing Children

Historically, growing children with a malignant bone tumor were treated by amputation, not only because of poor local control but because no satisfactory solution had been found to overcome the anticipated limb length discrepancy. As in the adult, limb-sparing surgery under the appropriate circumstances has become an accepted alternative to amputation in children. The functional result of limb-sparing surgery in growing children when performed by an experienced surgeon has proven to be very effective and well accepted. There are several unique issues with respect to limb-sparing surgery in skeletally immature patients that should be considered: 1) a good quality of life, 2) assessment of future growth potential, 3) limb length discrepancy due to the loss of one or more growth plates, and 4) early closure of the adjacent unaffected growth plate as a result of stem insertion through the plate.

Assessment of Limb Length
Limb length discrepancy in skeletally immature patients requires special consideration. Familiarity with the concept and methods used to analyze skeletal growth is essential (Anderson et al., 1964). Steady growth occurs throughout life. Growth spurts start early in adolescence and cease at the age of 16 to 17 years for boys and 14 to 15 years for girls. Children in whom secondary sexual characteristics develop at an early age reach skeletal maturity at an earlier age. Initially, these children may be tall for their chronologic age, but the end result will be a shorter stature compared with their peers.

In the lower extremity, there are four epiphyseal plates that contribute to the growth of the limb. Most of the growth of the lower extremity is contributed by the plates around the knee: distal femur, 38%, and proximal tibia, 28%. The proximal femoral growth plate contributes 16%, whereas the distal tibia contributes 18%. The femur is longer than the tibia and contributes 54% of the total leg length. Limb-sparing surgery involving the knee joint may include sacrifice of both of the epiphyseal plates, a loss of 66% of the future remaining growth.

There are several conditions that could slow down the epiphyseal growth rate. These include a change of the environment surrounding the plate, epiphyseal injury, fracture, infection, and damage to the growth plate by pins, screws, or a stem from a prosthesis that crosses the adjacent unaffected plate. These conditions could lead to the formation of a bone bridge across the plate that leads to premature, partial or complete, closure of the plate. Conditions that lead to muscle atrophy, such as prolonged bed rest, muscle paralysis, and limb-sparing surgery with muscle loss, all may result in slowing down the growth rate.

Leg length equality at skeletal maturity is the ultimate goal. Children can compensate for minor leg length discrepancy. Shortening of less than 2 cm has no functional or clinical significance; a shoe lift on the short side can solve the problem. There is no concern of possible low back pain and structural deformity, including scoliosis and pelvic obliquity as a result of limb length discrepancy. However, scoliosis is almost never seen. Patients may experience a mild nonfunctional structural deformity or pelvic tilt. Patients after limb-sparing surgery with loss of the extensor mechanism at the knee, drop foot, or knee arthrodesis would benefit from mild shortening of 1 to 2 cm. The residual discrepancy facilitates clearing of the foot by the weak short leg during the swing phase of gait. Patients with knee arthrodesis or with a nonexpandable prosthesis in whom a discrepancy of up to 5 cm develops are best treated by using a shoe lift or by contralateral epiphysiodesis, provided that the child has sufficient growth potential to correct the discrepancy. Discrepancy of over 5 cm can be managed by bone lengthening.

Bone lengthening using external fixator techniques is a useful modality to correct limb length discrepancy. This technique has a significant complication rate, including pin tract infection, fracture, delayed union, and potential neurologic deficit. This lengthening method has a limited use when a long endoprosthesis is present in the same bone. With the introduction of the expandable prosthesis, limb equality can be maintained by serial lengthenings.

After limb-sparing surgery, young children are expected to have some limb length discrepancies. This problem should be addressed either by contralateral epiphysiodesis, bone lengthening, or by an expandable prosthesis. All of these lengthening concepts are invasive and can be combined in different modalities as needed.

Reconstruction of a large segmental defect in a growing child with loss of one or more growth plates poses a significant challenge. There is no single modality that satisfies the needs of all patients. Each reconstructive modality has its own advantages and disadvantages. All options should be taken into consideration on an individual basis. Factors that have great implications for the long-term outcome of limb sparing that are not controlled by the surgeon are age, location, tumor extension, surgical staging, and level of resection.

Taking into consideration these criteria, the selected reconstructive modality should offer the patient the best realistic chance for survival and maximum functional result for the rest of the patient’s life, with a minimum of complications.

For a child with significant projected limb length discrepancy, the only options are an expanding prosthesis, rotationplasty, or amputation. If a child is near skeletal maturity, or the projected limb length discrepancy is less than 3 to 4 cm, a standard fixed-length reconstruction should be used for limb salvage. In this chapter, we discuss only expanding prostheses and rotationplasty.

The Expandable Prothesis
The application of recent advances in bioengineering and surgical oncology have led to great improvements in endoprosthetic design. Prosthetics are made small to be fitted to the child’s limb, and sufficiently durable to withstand the cyclic loading. In young children, one of the major concerns is to overcome the anticipated limb length discrepancy as a result of loss of one or more growth plates. This problem was solved partially by contralateral epiphysiodesis to halt growth and correct small discrepancies (Blair et al., 1982). In young patients, epiphysiodesis can result in a major shortening. Another solution to the problem was to perform bone lengthening using an external fixation device. This concept is effective; however, lengthening cannot always be applied in combination with internal prosthetics.

To address the problem of future limb length discrepancy, several telescoping endoprosthetic components were introduced. All require an invasive surgical procedure. Different kinds of modular components were suggested. These could be assembled together, using universal connection joints or Morse taper attachment.

An innovative approach to the problem by the introduction of expandable components was initiated in 1976 by the Biomedical Engineering Department at the Royal National Orthopaedic Hospital (Stenmore, United Kingdom). The Mark I was designed with a screw extension mechanism. The Mark II was lengthened by using a ball bearing mechanism.

The Lewis expandable adjustable prosthesis was introduced in 1983. This concept uses a screw extension mechanism. The prosthesis is made of a hollow titanium alloy tube assembled over a threaded shaft and fitted by a ring nut that can be rotated using a chuck key. The expansion capability of the prosthesis depends on the resection length. The prosthesis can be adjusted at the time of reconstruction to match the length of the resection. Lengthening is an invasive procedure that usually requires an overnight stay in the hospital. Complications can be expected along the way, and full cooperation and understanding of the procedure by the patient and family is needed. The compliance and emotional stability of the patient and parents are essential.

A major potential problem of limb-sparing surgery in young children is early closure of the adjacent uninvolved growth plate as a result of the insertion of the stem through the growth plate at the time of the reconstructive procedure. To avoid such complications, a passive telescoping component was designed by the Birmingham bone tumor treatment service. The passive spacer is made of polyethylene and is inserted through the growth plate to be firmly fixed at the metaphyseal region. A long metal stem is slid into the polyethylene sleeve. As the child grows, the metal stem is pulled out, allowing continuous growth. In some cases we have observed a continuous growth when a tibial component attached to the smooth polyethylene stem was crossing the growth plate. However, in many other cases we have seen partial or early closure of the growth plate as a result of hardware crossing the growth plate.

To avoid such a complication, in properly selected young patients, we have performed partial endoprosthetic replacement of only one side of the knee joint, without interfering with the other side of the joint. The prosthesis is practically sitting over the articular cartilage, as seen in hip bipolar prostheses. In children younger than 5 years of age in whom we can obtain enough stability, we have tried this approach successfully. To improve stability, range of motion at the knee is limited.

Lengthening Procedure
Lengthening is an invasive surgical procedure that requires an overnight hospital stay. Once limb length discrepancy exceeds 2 cm, lengthening is indicated. The amount of lengthening varies from 1.5 to 2 cm at a time, and could be repeated as needed once or more a year. The limiting factor for lengthening is the thick fibrous membrane around the endoprostesis, which resists stretching. In some cases, this membrane has to be transected to facilitate lengthening. After lengthening, a relative muscle shortening can occur, resulting in a temporary loss of range of motion that can be overcome by physiotherapy.

The surgical procedure is performed under general anesthesia through a longitudinal skin incision 4 to 5 cm in length over the lateral aspect of the thigh for a distal femur prosthesis, or over the medial aspect in cases of proximal tibial prostheses. Dissection is carried down through the fibrous membrane. The expansion mechanism is exposed widely. The locking screw and the ring nut are released. At this stage, using a chuck key, the key is rotated clockwise for lengthening. The motion of the ring is transferred to a threaded shaft, which is lengthened. At the end of the procedure, patients should be examined neurologically for possible neurologic deficiencies, drop foot, or loss of sensation. In 20 patients who had serial lengthening, no neurologic complications were seen with lengthening of up to 2 cm.

The total lengthening capability of each prosthesis is varied and depends on the amount of the resection. The larger the resection, the bigger the lengthening capability. The prosthesis should have at least 6 cm of lengthening capability. Once the entire threaded shaft is lengthened, usually after three lengthenings, a new prosthesis should be placed. Because all the components are press fit, they are easily replaced.

Ten Years’ Clinical Experience With the Expandable Prosthesis
Between 1983 and 1992, 60 pediatric patients with high-grade malignant bone tumors underwent limb-sparing surgery using the expandable prosthesis. Osteosarcoma was present in 48 children, Ewing’s sarcoma in 10, malignant fibrous histiocytoma in 1, and synovial sarcoma in 1 patient. There were 31 boys and 29 girls, ranging in age from 3 to 16 years. Twenty-two children were between the age of 4 to 8 years. Sixteen children were between the age of 9 to 12 years, and 22 children were between 13 to 16 years of age. Anatomic distribution included 24 in distal femur and 5 in proximal femur; 8 patients underwent total femoral replacement, 1 intercalary femoral replacement, and 15 proximal tibial and 7 proximal humeral replacement. Myocutaneous free flap for adequate prosthetic coverage was used in 15 patients. All patients received preoperative neoadjuvant chemotherapy. Three patients with Ewing’s sarcoma were also treated with postoperative irradiation.

Forty-three patients are disease free and were followed from 2 to 10 years, 11 patients were followed from 8 to 10 years, 13 patients were followed from 5 to 7 years, and 19 patients were followed from 2 to 4 years.

From the entire group of 60 patients, there were 3 local recurrences (5%), 2 of which initially presented with lung metastases. All three underwent above-the-knee amputation and subsequently died. Two other patients had early complications of infected prostheses that required above-the-knee amputations.

Of the 43 surviving patients, 19 were successfully revised (14 because of aseptic loosening and bone stem migration, 4 because of late infected prosthesis, and 1 because of a broken prosthesis). Twenty-two patients underwent serial lengthening from 2 to 10 cm. Functional assessment was performed using the criteria and rating scale recommended by the Musculoskeletal Tumor Society.

With respect to the proximal femur replacement, the functional results were good. Maintaining limb length equality was not difficult. The main problem in younger patients was femoral head subluxation because the shallow acetabulum containment of the femoral head was difficult to maintain.

With respect to distal femoral replacement, active quadriceps extensor mechanism was maintained in most cases. In young patients who had early closure of the adjacent unaffected growth plate as a result of stem insertion, it was difficult to maintain equality of limb length. Such a complication, in two patients, required bone lengthening of the tibia. In these patients with intact patellar tendons, it was difficult to regain knee flexion. However, the average functional results were good.

With respect to the proximal tibia, limb sparing required large osseous and soft tissue resection. In most patients, no attempt was made to reconstruct the extensor mechanism. Transposition gastrocnemius muscle flap or myocutaneous free flap was required to obtain adequate coverage. Patients with loss of the extensor mechanism had full passive extension and full active flexion. Most of these patients were able to walk without the need for crutches or braces. Patients in whom the extensor mechanism was reconstructed were able to obtain partial active extension. However, the weak flexor muscles could not overcome the knee extensor mechanism and, as a result, could not regain full flexion. The average functional result was rated fair.

With respect to proximal humeral replacement, the functional results were good. A discrepancy of up to 5 cm was well tolerated and had no functional impairment. In these patients, the prosthesis acted as a passive spacer, permitting strong active motion at the elbow and wrist. Restoration of shoulder stability and mobility is the most difficult and challenging problem. In an attempt to restore stability, we have introduced a new approach in prosthesis design, the reverse bipolar modular prosthesis. The metal spherical head is attached to the glenoid by screws. A reverse bipolar cup is then snapped on the head, and the bipolar cup is attached to the midsection. This prosthesis provides a fixed full arm to allow adequate, stable passive range of motion. This concept was used successfully in three patients with excellent results at 2 years’ follow-up.

Mechanical failure of the expandable mechanism in the early series of patients prevented lengthening in three patients. Improved designs in the expansion mechanism have allowed a more reliable mechanism. Our results with the use of the expandable prosthesis for the last 10 years showed satisfactory results. This invasive method of expansion is recommended until a better, noninvasive solution is found.

Implant Fixation
Durability of prosthetic fixation in long-term surviving children remains an unsolved problem. Both mechanical and biologic factors have been implicated in prosthesis loosening. The problems encountered with artificial joint replacement in adults are greatly intensified in skeletally immature patients. Children undergo continuous three-dimensional bone remodeling and a continuous change in the shape and size of the medullary cavity, affecting prosthetic fixation. As a result of resection of a large segment of bone and muscle, there is a change in the applied forces, subjecting the prosthesis and its fixation medium to axial bending and torsional loading, which result in compressive tensile and shearing forces. The end result is bone stem migration. The two most important factors affecting long-term fixation are excessive motion and the formation of particulate debris. These two factors are associated and can act synergistically. In the last few years, it has become evident that particulate debris plays a major role in the process of aseptic loosening. Debris-mediated osteolysis had been the most serious problem in component failure, resulting in deficient bone stock and complex revision procedures.

In growing children, loosening and bone stem migration are almost inevitable. Most children, after limb-sparing surgery, should expect a revision procedure. The main problem is how to maintain bone stock and delay future revisions. To improve prosthesis longevity, the problem of particulate debris should be addressed. All sources of debris should be minimized. Fixation of all components should be press fit, which as proven to be reliable and durable.

The problem of prosthetic fixation has not been solved. A better understanding of the mechanical and biologic processes, with design of new biocompatible materials in combination with biologic substitutes should increase prosthesis longevity.

Rotationplasty
Rotationplasty of the lower extremity, first described in the treatment of infection and later in the treatment of congenital deformities, is a functional and durable reconstructive option after the resection of a malignant bone tumor. This is especially true in the treatment of patients who are skeletally immature. Recurrence rates are comparable with those after other forms of wide resection. With preoperative education of the parents and the child and with proper patient selection, this procedure is a well accepted and functional alternative to either transfemoral amputation or endoprosthetic replacement.

For a child with a malignant bone tumor about the knee, surgical options include hip disarticulation, transfemoral amputation, or wide resection followed by either expandable endoprosthetic replacement or rotationplasty. Fixed-length reconstructions such as osteoarticular allografts, allograft-arthrodeses, or nonexpandable prostheses are not considered here. With regard to local tumor control, wide amputation, wide resection and rotationplasty, and wide resection and expandable prosthesis are associated with a low incidence of local recurrence in most cases. However, in those instances in which there is tumor involvement of the vascular structures, obvious intra-articular disease, or a difficult biopsy re-excision site, rotationplasty offers wider margins than would be available if an endoprosthesis were selected. In addition, rotationplasty can also be considered as a salvage procedure after a failed endoprosthetic replacement. As with any form of limb salvage surgery or tumor reconstruction, contamination of the tibial nerve is a contraindication to the performance of rotationplasty.

Functionally, rotationplasty compares favorably with either transfemoral amputation or endoprosthetic replacement. Gait velocity, although slow compared with that of normal individuals, is similar to or increased over that of patients with endoprostheses, and is increased compared with that of patients with amputations. The energy cost is less for those patients with rotationplasty or an endoprosthesis than for amputees. Electromyographic testing demonstrates that the phasic activity of the rotated posterior calf musculature coincides with that of the quadriceps, as is the case for the anterior calf muscles and knee flexors. No specific training of the transposed muscle groups is necessary. The rotated ankle and foot function as a knee and proximal tibia, although obviously with less strength and stability than in the native situation. Compared with patients with a transfemoral amputation, patients with rotationplasty have an end-bearing prosthesis and improved gait efficiency.

Rotationplasty has been demonstrated to be a durable reconstruction, and the patients, with prosthetic adjustment, are able to participate in a broad range of recreational and sports activities. In contrast, patients with an endoprosthesis are, in general, advised against engaging in rigorous activities to avoid prosthetic complications and loosening.

A common complication related to the procedure is vascular compromise. This is especially true in patients requiring anastomosis of vessels. Other complications in the immediate postoperative period include a transient or permanent nerve palsy, delayed would healing, infection, rotational malalignment, and compartment syndrome. Late complications include pseudarthrosis and fractures. Spontaneous derotation, described in children with congenital limb deformities, has not been reported in patients who have malignant disease. Despite the complications, most patients require no further surgery. Unlike an amputation, this procedure does not result in the formation of a painful neuroma, nor is any phantom pain associated with the procedure.

Obviously, however, the appearance of a rotated limb and the reaction to it by the patient, his or her family, and society raise the possibility of significant psychosocial problems. However, as in patients with amputations, with preoperative education of the family, including photographs, literature, and introduction to patients with similar circumstances, permanent and severe psychosocial damage is not expected, nor has it been reported, in patients with malignant tumors. Serious consideration, however, should be given to certain culture-, age-, and sex-specific expectations and desires. There has been no described impact on the ability to pursue higher education, locate and keep a job, or develop relationships. For these reasons, rotationplasty remains an excellent alternative in the treatment of malignant tumors of skeletally immature patients. It is functional, durable, and, in most cases, associated with a favorable oncologic outcome.

Surgical Technique
The technique described is for the case of a malignant tumor of the distal femur, but it is generally applicable to tumors of the proximal tibia as well.

Preoperative preparation of the patient and family as well as careful surgical planning are essential for the successful performance of the rotationplasty. A thorough discussion with the family is imperative, including the options of amputation or of an expandable prosthesis, the relative risks and benefits of each procedure, the expectations of the patient and family, photographs of the surgical results, and communication with a similarly treated patient.

Once rotationplasty is decided on, limb length films of both lower extremities are obtained. In addition, bone age should be approximated by use of hand film and the standard bone atlas. With this information, and with a graph for determining limb length growth, an estimation can be made with regard to the final projected growth of the normal limb compared with the operated limb. We recall at this point that the distal femoral and proximal tibial growth plates will be removed with the tumor specimen. The goal of this surgery is that, at the time of skeletal maturity, the rotated tibial talar joint of the operative limb will be at the projected center of rotation of the knee of the nonoperated limb. At the time of surgery, therefore, the operated leg should be longer than the nonoperative femur. The growth rate difference is the difference between the growth of the unoperated distal femoral epiphysis and the operated distal tibial epiphysis. Kotz and Salzer (1982) recommended approximately 6 cm of additional length in the operated limb of a 6-year-old and 4 cm in a 10-year-old child.

The next step is to measure the extent of the tumor as seen on preoperative magnetic resonance imaging. A bone resection of the distal femur should be planned approximately 3 to 4 cm proximal to the most proximal extent of the tumor. Knowing the amount of bone to be resected, the amount of proximal femur remaining, and the projected length of the nonoperated femur, the surgeon can calculate the amount of tibial resection.

Preoperative imaging is important for determining whether the tumor involves the joint itself or the posterior vascular structures. If there is a possibility that the joint is contaminated, extra-articular resection is recommended. If the vessels are involved, a vascular resection and anastomosis is necessary.

After this careful preoperative evaluation, the patient is brought to the operating room and placed in a supine position. After anesthesia is administered, prophylactic antibiotics are given and are continued postoperatively until all drains have been removed. The patient’s hind-quarter is sterilely prepared and draped in the usual fashion, allowing access to the lower quadrant of the abdomen. The limb itself is draped free. A sterile tourniquet may be used; however, because the leading cause of immediate postoperative complications are thrombosis and limb ischemia, a tourniquet is not recommended.

Because of the disproportion between the thigh and calf circumference, the skin incision must be carefully planned. A commonly used incision is a rhombus with its long axis anteriorly, placed at a distance 5 to 10 cm greater than the intended length of the bone resection. The bone resection itself should be placed in the junction of the proximal and middle thirds of the more proximal incision. A second incision is made distal to the tibial tuberosity, and is again a circumferential incision, but at a more acute angle in the longitudinal access of the limb, as depicted. This allows and compensates for the difference in circumference between the thigh and calf. A posterior or lateral linear incision that connects the proximal and distal incisions is then made.

Gebhart and colleagues (1987) described an alternative skin incision. A transverse circumferential thigh incision is made proximally at mid-thigh, and a fishmouth skin incision is made distally at the proximal calf. The length of the medial and lateral longitudinal portions of the fishmouth incision should be one fourth the difference between the thigh and calf circumference, and would approximate 2.675 cm on the average. This incision allows wound closure without constriction or irregularities. Skin and subcutaneous tissue are divided, and flaps are carefully raised initially laterally and then medially, care being taken not to undermine the biopsy site. The peroneal nerve is approached first. It is identified exiting from deep to the biceps tendon and coursing laterally about the proximal fibula. It is dissected free of surrounding soft tissue in its subcutanceous location and is followed proximally into the posterior thigh and distally into the anterior compartment of the leg. Dissection of the peroneal nerve is carried out proximally until the bifurcation between it and the tibial nerve is identified. At this point, the tibial nerve is dissected distally into the popliteal space and distal to the proposed tibial osteotomy site. The nerve dissection is then carried proximally from the bifurcation that identifies the sciatic nerve well proximal to the level of the femoral osteotomy. At this point, the crossing long head of the biceps should be divided at the level of the sciatic nerve.

Attention should then be turned medially, where transection and reflection of pes anserinus tendons and the medial head of the gastrocnemius reveals the popliteal artery and vein. Beginning at the level of the popliteal artery, segmental branches to the gastrocnemius and posterior knee are ligated so that the vessels can be freed from the surrounding soft tissues. It is essential to free the vessels of all surrounding soft tissue to prevent kinking and tension on the vessels during the later rotation. These vessels are traced distally to the level of the trifurcation. Proximally, the dissection brings the popliteal artery and vein away posteriorly from the femur and through the adductor hiatus, where the tendon of the adductor magnus is transected well away from bone. Vessel dissection is continued more proximally to a level proximal to the proposed osteotomy site.

If the vessels are to be resected en bloc with the tumor specimen, they are identified proximal to the level of the femoral resection and distally in the region of the popliteal vessels, distal to the tumor itself. Enough exposure is obtained in the vessels to allow them to be cut and reanastomosed after the rotation. They are not ligated, however, until the tumor is ready to be removed from the wound.

Once the sciatic, tibial, and peroneal nerves as well as the popliteal vessels have been identified and freed of surrounding soft tissues, preparation is made to perform the osteotomy. At the apex of the incision, well proximal to the proposed level of bone resection in the femur, a Steinmann pin should be placed from anterior to posterior with the patella directed anteriorly. This pin should be placed well proximal to the anticipated level of bone resection to allow for additional shortening, should this be required. Distally, in the region of the tibia, a second Steinmann pin is placed from the medial aspect of the tibia, exactly perpendicular to the femoral pin placement. This pin, again, should be placed well distal to the surgical incision and may be placed percutaneously. At this point, returning to the region of the proximal femur, the quadriceps and hamstrings are transected in line with the skin incision, while the neurovascular structures are protected.

If an intra-articular resection is planned, the knee is flexed and the patellar tendon is transected at its insertion on the tibial tubercle. The proximal tibia is then exposed below the meniscal tibial ligament, leaving the menisci with the femur. The anterior and posterior cruciate ligaments are transected at their insertion on the proximal tibia, leaving the bulk of the ligament with the femur as well. This can be facilitated by elevation of the medial collateral ligament from the tibia medially. The surgeon may obtain further exposure by releasing the biceps tendon insertion and the lateral collateral ligament from the head of the fibula. The tibia is then translocated anteriorly with respect to the femur, and the posterior knee capsule is released at its tibial insertion. Finally, while the neurovascular structures are protected, the lateral head of the gastrocnemius is transected through its muscle belly at the level of the knee joint. This allows the femur to be brought anteriorly and out of the wound. The neurovascular structures should be in continuity posteriorly between the proximal thigh and leg. Measuring from the region of the distal femur, the anticipated bone resection level is identified, and an oscillating saw is used for performing an osteotomy. At this point, the distal femur along with the surrounding soft tissue can be removed from the wound.

The proximal tibia is then subluxed anteriorly, while the posterior neurovascular structures are protected, and a proximal tibial osteotomy is performed distal to the physis. Similarly, the proximal fibula is identified while the anterior interossseous neurovascular bundle and the peroneal nerve are protected, and the proximal fibula is resected at the same level. Although no difficulties have been described in retaining the proximal fibular physis, it is probably wise to osteotomize the fibula distal to the growth plate, as is done with the tibia.

However, if there is concern about a potential intra-articular tumor, then an extra-articular resection should be performed. In this instance, the proximal tibia is osteotomized, protecting the posterior neurovascular structures at the level of the tibial tuberosity. Attention can then be turned to the proximal fibula and to protecting the anterior interosseous vessels, and the peroneal nerve and the fibula can be taken at the same level. The distal femur and proximal tibia can then be removed en bloc with the accompanying extensor mechanism without the need for an arthrotomy.

After negative marrow margins and suspect soft tissue margins are examined by frozen section, the wound is irrigated. The vessels are examined for confirmation of adequate flow, and any arterial spasm may be partially reversed with topical administration of papaverine.

The reconstruction consists of externally rotation the tibia through 180&Mac251; so that the tibial pin now is perpendicular to the femoral pin from the lateral aspect of the limb. The vessels ordinarily coil medially as the rotation is completed. Any kinking in the vessels may indicate adherent soft tissues, which prevent adequate rotation. The tibial and peroneal nerves should be examined to ensure that there is no excessive tension on them after the rotation. An assessment is made of the overall length of the limb, confirming adequate rotation. If additional shortening is required, either additional bone may be resected or the femur may be countersunk into the proximal tibia metaphysis. The lateral aspect of the femur and the medial aspect of the proximal tibia are then exposed to allow compression plating of the junction. A six- or eight-hole 4.5 DC plate is recommended. In addition, if an intra-articular resection was performed, bone from the resected proximal tibia can be used as a local bone graft. An intraoperative radiograph is recommended so that the overall alignment of the limb can be viewed. A small amount of anterior bowing, recreating that of the normal femur, and a slight valgus for maintaining a horizontal tibiotalar joint are acceptable positions.

If the vessels were sacrificed with the tumor, an anastomosis should be carried out at this time. Two deep drains are placed in the wound, and the quadriceps mechanism is sutured to the gastrocnemius muscle belly and to the deep fascia of the calf. The hamstrings are sutured to the pretibial fascia. The wound is closed in multiple layers, and a bulky compressive dressing is applied so that the sometimes significant edema seen in the distal extremity is minimized. Because the fixation is rigid, no cast is necessary. Instead, active motion of the hip and ankle is encouraged as soon as possible.

It is imperative, especially in cases of vascular repair, to observe the circulatory status of the limb closely. In addition to being monitored for ischemia, the patient should be monitored for the development of a compartment syndrome.

When the patient demonstrates adequate wound healing, usually between 2 and 6 weeks, a temporary ischial weight-bearing prosthesis with an external hip joint may be fitted. No weight bearing through the osteosynthesis junction should be attempted until there are radiographic and clinical sighs of healing. This is especially true for individuals undergoing chemotherapy, because healing may be delayed. Once the osteosynthesis site has healed, a prosthesis allowing distal weight bearing and motion through the ankle is made and worn. External hinges about the ankle offer varus and valgus stability to the ankle. The patient is allowed activity as tolerated at this time.

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