3. Adult Reconstruction (Hip & Knee) MCQs

DISCUSSION: The patient has symptomatic grade IV Brooker heterotopic ossification. Once the bone has matured, it can be excised. Surgical excision should be combined with postoperative irradiation to avoid recurrence. Pharmacologic and irradiation intervention are not successful beyond the perioperative period unless they are combined with surgical excision of mature heterotopic ossification.

DISCUSSION: The radiograph shows a loose femoral component with failure of osseous integration. There is a reactive radiolucent line around the fiber mesh portion of the implant, hypertrophy of the bone under the collar, and a pedestal formation at the distal tip of the implant, all of which indicate failure of bone ingrowth. If bone ingrowth had occurred, there would be stress shielding of bone under the collar.

Discussion: Wear in total hip arthroplasty is a very complex phenomenon. The radial mismatch of the femoral head to the acetabular component has been shown in multiple studies to be a significant factor in wear. The mismatch can neither be too small nor too large. When the mismatch is too small, seizing of the implants can occur. When the mismatch is too large, contact stresses increase and produce exceptionally high wear. The ideal radial mismatch should be approximately 50 microns. Surface roughness and ball sphericity are two items that are extremely important with respect to wear. High carbon content has been shown to decrease wear. This device has a very large head-to-neck ratio, so impingement-related wear is unlikely.

Discussion: THA has proven durable and reliable for pain relief and improving function for patients with end-stage arthritis. Appropriate bearing selection is critical to minimize wear and hip complications. A metal-on-metal articulation is associated with excellent wear rates in vitro. With its capacity to offer a low wear rate with large femoral heads, it is an attractive bearing choice for THA. However, local soft-tissue reactions, pseudotumors, and potential systemic reactions including renal failure, cardiomyopathy, carcinogenesis, and potential teratogenesis with potential transfer of metal ions across the placental barrier make metal-on-metal bearings less desirable and relatively contraindicated for younger women of child-bearing age.

Discussion: The plain radiograph shows a defect in the lateral femoral condyle and narrowing of the lateral joint space. The MRI scan shows a lesion consistent with osteonecrosis of the lateral femoral condyle. The treatment alternatives for this condition are an osteotomy or a total knee replacement, but a total knee replacement is the treatment of choice for a 72-year-old patient. Arthroscopy or an osteochondral bone graft will not address her symptoms. A valgus osteotomy will exacerbate the problem by overloading the lateral joint, which is already diseased.

The current recommendation for antibiotic prophylaxis for major orthopaedic surgical procedures is to administer intravenous antibiotics within 1 hour of surgical incision. Redosing of antibiotics should occur 3 to 4 hours after the initial dose for procedures that extend beyond 3 to 4 hours. Little evidence supports postsurgical antibiotic use beyond 24 hours. As you move beyond 1 hour from time of administration of antibiotics, risk for infection increases and rates of bacterial cell death decline. It is not acceptable to administer presurgical antibiotics after incision.

Discussion: A patient with an infected total hip arthroplasty may lack the symptoms of fever, chills, redness, or increased warmth typical of septic arthritis. Sensitivity for ESR and CRP ranges from 61% to 96%, and specificity ranges from 85% to 100%. Technetium Tc 99m bone scans are costly and time-consuming and will not differentiate between septic and aseptic loosening. Hip aspiration has a false-positive rate of up to 15%, although it may be useful in this patient to further complement the clinical picture if the ESR and CRP are elevated. The WBC count is rarely elevated in infected total hip arthroplasty. MRI is expensive and is not indicated for the diagnosis; however, it can aid in identifying intrapelvic extension of a periprosthetic abscess.

Stress relief changes seem to be most strongly related to component stiffness. However, stress relief changes are probably multifactoral and involve stiffness, location and extent of porous coating and the presence or absence of a collar. Host factors also influence stress relief.

Elbow instability after placement of an unconstrained implant is most often the result of ligamentous insufficiency that can occur late after the index procedure. Instability can also occur from component malpositioning that creates undue stress to the collateral ligaments during the life of the prosthesis. Instability leads to revision surgery in many patients. Polyethylene wear and bushing wear are more common in linked and semiconstrained elbow arthroplasties. Loosening of humeral components may occur with aseptic or septic disease. Component fracture is uncommon.

Periprosthetic fractures are the third-most-common reason for revision surgery after total hip arthroplasty (THA). Risk for concomitant infection in the presence of a periprosthetic fracture is 11%. Obtaining presurgical aspiration or tissue for culture intrasurgically is recommended if concomitant infection is suspected. In a patient with a periprosthetic fracture, ruling out infection is a critical step in the workup.

This patient likely is experiencing failure of his UKA secondary to poor patient selection. This young, heavy man likely loosened his component secondary to the ongoing varus alignment of the knee and his elevated weight. Despite this likely scenario, the next step is to determine if an infection is the cause of his pain. Prior to obtaining an aspiration, the surgeon can order an ESR and CRP to determine if aspiration is warranted. If laboratory studies are unremarkable, the surgeon likely can forgo the aspiration and proceed to a revision TKA with possible augments on standby.

The radiograph shows three zones: an outer regenerated cortical layer, an interface zone consisting of viable trabecular bone and occasional particles of bone cement, and an inner layer of necrotic bone embedded in cement. No fibrous membrane is noted, and there is no direct contact of cement with native bone. Based on these findings, it is believed that the middle layer is the result of incorporation of the allograft with further remodeling.

Discussion: The answer to this question is based on a study by Harris which tested the effeciency , rate and percent of max rate in ambulation in amputees, those with arthrodeses and arthroplasties. They found that Above knee amputees expended the most energy, followed by arthrodesis patients, and then arthroplasty patients.

Discussion: This patient has a chronic quadriceps tendon rupture after total knee arthroplasty. Two previous primary repair attempts have failed. The patient also has an unstable knee and will require revision of some or all of the prosthesis to achieve a stable knee. Revision total knee arthroplasty with extensor mechanism allograft allows an allograft reconstruction of the ruptured quadriceps tendon. Two-stage revision total knee arthroplasty with extensor mechanism allograft is not the best option because the laboratory results show no signs of infection, so a single-stage procedure is preferred.

Discussion: The prevalence of postoperative ileus associated with total joint arthroplasty has been reported to be as high as 3%. Metabolic abnormalities such as hypokalemia are believed to contribute to the onset of ileus and Ogilvie’s syndrome (acute pseudo-obstruction of the colon). Prolonged bed rest also has been associated with the development of ileus and Ogilvie’s syndrome.

Long term prospective study involving 67 humeral head replacements for OA &RA. "Based on this experience, we would recommend that humeral head replacement alone be used sparingly in patientswith OA or RA. Certainly in patients who have glenoid bone deficiency precluding placement of a glenoid component…" as is apparent in this radiograph.

Sudden death during total hip arthroplasty has been reported. In a report from the Mayo Clinic, intraoperative death occurred during cemented total hip arthroplasty in 23 patients. Fat and marrow embolization during preparation of the femur or cementing of the femoral component was believed to be responsible for the cardiopulmonary collapse that occurred during arthroplasty. Although fat and marrow emboli were found in the pulmonary capillaries of most of the patients on autopsy, this histologic section shows two particles of cement in the pulmonary capillaries.

DISCUSSION: The most appropriate bearing of those listed would be a large diameter metal head on cross-linked polyethylene. Because of the renal insufficiency, metal-on-metal should be avoided because metal ions are renally excreted. Ceramic-on-ceramic implants are not necessary in this patient because of the patient’s limited activity and life expectancy, as well as the downside of increased cost, the small but definite risk of ceramic fracture, and the increased technical demands of inserting ceramic implants. A highly cross-linked liner is favored to allow for maximum head size as the patient may be at increased risk of dislocation because of his neurologic disorder. REFERENCES: Bragdon CR, Greene ME, Freiberg AA, et al: Radiostereometric analysis comparison of wear of highly cross-linked polyethylene against 36- vs 28-mm femoral heads. J Arthroplasty 2007;22:125-129. MacDonald SJ: Metal-on-metal total hip arthroplasty: The concerns. Clin Orthop Relat Res 2004;429:86-93.

The radiograph shows a well-osseointegrated tapered stem with a metaphyseal porous coating, spot welds in the porous region, and calcar rounding. Trochanteric stress shielding and distal cortical hypertrophy are also signs of ingrown stems but are seen more frequently in association with extensively porous-coated stems exhibiting diaphyseal ingrowth. There is no evidence of lucent lines or a pedestal, signs that suggest instability. Femoral stem subsidence can be determined only by a review of sequential radiographs.

The theoretic total knee components will resist anteroposterior motion by making the femoral component “climb the walls” of the tibial component. As drawn, there is no constraint to medial-lateral translation. The cylinder is not rounded on the edges, so varus-valgus motion will impart load from the cylinder to the trough over a small area, thus having a high contact stress.