3. Adult Reconstruction (Hip & Knee) MCQs

Trunnionosis is a recently recognized complication following total hip arthroplasty and can occur when a cobalt alloy femoral head is used on a titanium alloy or cobalt alloy femoral stem. Patients often present with pain or swelling around the hip but at times can present with instability. Certain femoral stem designs have been associated with increased reports of trunnionosis. In a patient with a cobalt alloy femoral head who presents with instability, swelling, and weakness around the hip, the potential for trunnionosis and an adverse local tissue reaction should be considered.

During osteolysis, IL-6 is secreted by fibroblasts in the membrane surrounding the prosthesis. IL-6 also can be secreted by osteoblasts in other settings, but they are not the predominant source of IL-6 in particle-induced osteolysis. The remaining cells are not major sources of IL-6.

Emboli are created during TKA. Usually there is an increased incidence with the use of intramedullary rods that disrupt the marrow contents. These are not fat emboli per se. They are material composed of fat cells and marrow that act like pulmonary emboli to obstruct small arterioles in the lung. They are different from free fat emboli that are seen in fractures and that lead to chemical injury to the lung rather than obstructive injury.

DISCUSSION: Injury to the sciatic nerve is a relatively rare but serious complication of THA. Dissection of the sciatic nerve is not typically done during primary THA, although the nerve can be identified during the surgical approach. An anterolateral approach to THA would not necessarily be associated with any greater incidence of sciatic nerve injury than other approaches. Screw fixation for the acetabular component is often a matter of surgeon preference. Provided that the anatomic safe zones for screw fixation (posterior inferior and posterior superior) are recognized, injury to the sciatic nerve from acetabular screws can be minimized. Restoration of anatomic length is important in primary THA. Overlengthening can result in sciatic nerve palsy. Developmental dysplasia of the hip can lead to a congenitally shortened extremity with concomitant congenital shortening of the associated neurovascular structures. Overlengthening of the extremity during THA for developmental dysplasia of the hip can lead to sciatic palsy. Osteonecrosis is not an associated risk factor for sciatic nerve palsy. REFERENCES: DeHart MM, Riley LH Jr: Nerve injuries in total hip arthroplasty. J Am Acad Orthop Surg 1999;7:101-111. Anas P, Felix B: Evaluation and prevention of postoperative complications, in Neurologic Injury in Revision THA. New York, NY, Springer Verlag, 1999, pp 361-371.

DISCUSSION: Stems are available for cemented and press-fit implantation. To be effective, press-fit stems should engage the diaphysis, as shown in Figures 3 and 4. They also assist in obtaining correct limb alignment. Short metaphyseal-engaging stems are associated with failure rates that range between 16% and 29%. Cemented stems may be shorter than press-fit stems, because they do not have to engage the diaphysis. Short, fully cemented stems offer the advantage of metaphyseal fixation. Hybrid stem fixation makes use of the metaphysis for cement fixation with metaphyseal cones or sleeves and diaphyseal-engaging press-fit stems.

DISCUSSIONThis patient presents with significant polyethylene wear, which can lead to both osteolysis and synovitis. However, synovitis usually manifests as a mild to moderate chronic ache, which should explain the discomfort. Although infection should always be ruled out with new-onset pain, no clinical parameters suggest acute hematogenous infection. Similarly, without any mention of back pain or neuropathy, radicular pain from the spine is unlikely. If this patient has a nondisplaced greater trochanteric fracture noted on MR imaging, the optimal immediate mode of treatment is to not rush into surgery despite the mild osteolysis. The patient’s severe pain is likely attributable to the nondisplaced greater trochanteric fracture rather than wear-induced synovitis, which typically presents as a mild to moderate ache. It is recommended toallow the fracture to heal to avoid fracture displacement. Once the fracture is healed, a revision surgery with liner exchange can be recommended. Based on this clinical scenario, the acetabular component is within what is largely considered the “safe-zone” in THA. Despite this patient’s dislocations, the preferred treatment modality is to revise to a constrained liner. This patient had a well-functioning hip for longer than 15 years. Therefore, conversion to a constrained liner is the best treatment.

DISCUSSION: Obesity, a prior history of venous thromboembolism, and metabolic syndrome have all been associated with an increased risk of thromboembolism. A recent meta-analysis showed that diabetes had no significant relationship with venous thromboembolism following hip or knee arthroplasty. Tranexamic acid is an antifibrinolytic agent that has been shown to reduce blood loss substantially following hip and knee arthroplasty. It has also been shown to be safe in patients with severe medical comorbidities and a prior history of venous thromboembolism.

Alternative bearing surfaces in THA have received much attention in recent years as more and more hip arthroplasties are being performed on younger patients with hip arthritis. The two most popular nonmetal-on-polyethylene bearing surfaces are metal-on-metal and ceramic-on-ceramic. There are arguments supporting the use of either, but ceramic bearings have been shown to have a theoretic increased risk of fracture compared with cobalt-chromium. This has been shown to be clinically relevant with zirconium ceramics. Newer alumina ceramics are being produced with lower porosity and grain size and with higher density and purity, resulting in lower fracture risk but still greater than that of cobalt-chromium.

DISCUSSION: Varus position of the stem is most commonly associated with failure of the cemented femoral component because of association with an inadequate cement mantle in the proximal medial and distal lateral zones. An inadequate cement mantle and obesity have been associated with increased loosening but not as frequently as a varus deformity. The influences of gender and osteoporotic bone on the outcome of cemented femoral components have not been established.

DISCUSSION: Positioning of the femoral and tibial components is a common cause of early failure of total knee arthroplasty. Two modes of possible position are raising or lowering the joint line from its anatomic level. Raising or lowering the joint line beyond an established threshold can cause limited range of motion, poor patellar function, and possible instability. It has been determined that a threshold of approximately 8 mm provides consistently good results after knee arthroplasty.

The recent experience of a large clinical cohort revealed the most likely risk factors as being female gender, age younger than 40, small components, and a diagnosis of hip dysplasia causing osteoarthritis. Failure was least likely among men and after procedures involving larger components. These data have prompted some authors to caution against using metal-on-metal hip resurfacing in women and to primarily target candidates who are men younger than age 50. Small components may be more prone to failure because of malpositioning and edge loading, which have been noted to be more common in dysplasia cases.

In patients with chronic progressive shoulder pain and glenohumeral osteoarthritis, the humeral head typically subluxates posteriorly, leading to maximal glenoid erosion in the posterior quadrant.

DISCUSSION:The patient has an extensor mechanism disruption with patellar tendon rupture. This injury is treated with extensor mechanism reconstruction in the setting of previous total knee arthroplasty. There is a reported high  failure  rate  with  attempted  repair.  Revision  to  hinge  knee  arthroplasty  would  provide  implant stability but would not restore the extensor mechanism. The patient is relatively young and is working, so reconstruction would offer better long-term function than a drop lock brace, which can be better used in low-functioning patients with this type of injury. Extensor mechanism reconstruction historically has been accomplished  with  allograft  material,  but  a  novel  technique  using  synthetic  mesh  also  has  proved successful in treating this difficult problem.

DISCUSSION: Numerous studies have documented the poor performance of heat-pressed ultra-high molecular weight polyethylene used in the porous-coated anatomic tibial inserts of both total knee and unicompartmental arthroplasty. The other processing and sterilization methods have not been associated with significantly high failure rates. REFERENCES: Wright TM, Rimnac CM, Stulberg SD, et al: Wear of polyethylene in total joint replacements: Observations from retrieved PCA knee implants. Clin Orthop 1992;276:126-134. Landy MM, Walker PS: Wear of ultra-high molecular-weight polyethylene components of 90 retrieved knee prostheses. J Arthroplasty 1988;3:S73-S85. Skyrme AD, Mencia MM, Skinner PW: Early failure of the porous-coated anatomic cemented unicompartmental knee arthroplasty: A 5- to 9-year follow-up study. J Arthroplasty 2002;17:201-205.

DISCUSSION: Given a well-fixed acetabular metal shell and a localized osteolytic lesion, good outcomes can be expected from liner revision in this clinical scenario with retention of the metal socket, assuming no damage to the components or other unexpected findings arise during revision surgery. Here, complete cup revision is not warranted, considering the appropriate implant position. Beaulé and associates reviewed 83 consecutive patients (90 hips) in whom a well-fixed acetabular component was retained in a clinical scenario such as the one described. No hip showed recurrence or expansion of periacetabular osteolytic lesions. If the metal cup is unstable, acetabular component revision may be indicated.

DISCUSSION: An assessment of the location of the vascular compromise is necessary prior to surgical exploration. Vascular repair will most likely require a separate surgical exposure. Vascular reperfusion may be accomplished at the time of an arteriogram with the use of a stent in certain situations. Return to the operating room with vascular surgical consultation and intraoperative arteriogram is appropriate. An immediate postoperative compartment syndrome is unlikely. Magnetic resonance angiogram is not appropriate because of the potential for a delay in diagnosis. REFERENCE: Smith DE, McGraw RW, Taylor DC, et al: Arterial complications and total knee arthroplasty. J Am Acad Orthop Surg 2001;9:253-257.

DISCUSSION:Controversy persists over what exactly is the best approach to managing patients with metal-on-metal (MOM)  hip  arthroplasties.  All  patients  with  painful  MOM  hip  arthroplasties  should  be  examined  for fixation  loosening,  wear/osteolysis,  and  infection—no  differently  than  patients  without  MOM  hip arthroplasties.  It  is  recommended  to  obtain  serum  trace  element  levels.  If  the  levels  are  high,  cross- sectional imaging should be obtained to determine whether any pseudotumor or tissue necrosis is present around the hip arthroplasty. Hip aspiration should be considered if concern for infection exists. Adverse tissue reaction has been identified to occur around MOM hip arthroplasties. The predominant histologic feature is tissue necrosis with infiltration of lymphocytes and plasma cells.

DISCUSSION: The radiographs show an oblique periprosthetic distal femoral fracture. Of the options listed, open reduction and internal fixation is the most appropriate surgical option because a well-fixed, posterior stabilized closed box femoral component is present. Nonsurgical methods are not favored because of the highly displaced, unstable fracture pattern and prolonged immobility. Revision with a stemmed component is an option but would sacrifice more bone stock in this younger patient. REFERENCES: Moran MC, Brick GW, Sledge CB, et al: Supracondylar femoral fracture following total knee arthroplasty. Clin Orthop 1996;324:196-209. Raab GE, Davis CM III: Early healing with locked condylar plating of periprosthetic fractures around the knee. J Arthroplasty 2005;20:984-989. Tharani R, Nakasone C, Vince KG: Periprosthetic fractures after total knee arthroplasty. J Arthroplasty 2005;20:27-32.

Ceramic-on-ceramic bearing surfaces have superior tribological properties and show lower linear wear than metal-on-metal implants. However, because of their lower strength and vulnerability to fracture, design considerations constrain the neck-length options available to ensure optimal taper fit.

TXA is easy to administer, inexpensive, and safe for virtually all patients. Multiple studies have demonstrated transfusion rates lower than 3% for total knee arthroplasty and lower than 10% for total hip arthroplasty. Regional and hypotensive anesthesia effectively reduce transfusion; however, they cannot be used in as wide a range of patients as TXA. A reduced transfusion trigger must be considered along with patient symptoms when determining the need for transfusion.