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Dislocation of posterior-stabilized mobile-bearing knee prosthesis
The Knee 13 (2006) 478 – 482 www.elsevier.com/locate/knee
Short Communication
Dislocation of posterior-stabilized mobile-bearing knee prosthesis A case report Masahiro Hasegawa ⁎, Akihiro Sudo, Aki Fukuda, Atsumasa Uchida Department of Orthopaedic Surgery, Mie University Graduate School of Medicine, 2-174 Edobashi, Tsu City, Mie 514-8507, Japan Received 12 June 2006; received in revised form 12 July 2006; accepted 23 July 2006
Abstract Spin-out of mobile-bearing knees is a significant early complication of mobile-bearing total knee arthroplasty. Dislocation of the cam-post mechanism of fixed-bearing posterior-stabilized knees occurs more rarely. We have observed an unusual case of dislocation of posteriorstabilized rotating-platform total knee arthroplasty, which has both a cam-post mechanism and rotating platform. A 65-year-old man with knee osteoarthritis and cervical spondylotic myelopathy underwent total knee arthroplasty using a mobile-bearing prosthesis. The dislocation, which occurred 4 days postoperatively, could not be reduced by closed manipulation. However, spontaneous reduction occurred 6 days after the dislocation, which did not recur. A gap mismatch or trapezoidal-shaped gaps may lead to dislocation or spin-out of the bearing insert. This case illustrates that dislocation of a posterior-stabilized mobile-bearing total knee arthroplasty can occur, and both quadriceps deficiency and ligament laxity may contribute to the risk of dislocation. © 2006 Elsevier B.V. All rights reserved. Keywords: Total knee arthroplasty; Dislocation; Mobile-bearing; Posterior-stabilized; Complication
1. Introduction In mobile-bearing total knee arthroplasty (TKA), congruency between the femoral component and the superior surface of the rotating polyethylene in a mobile-bearing design is intended to reduce polyethylene contact stresses, while rotation between the inferior polyethylene surface and the metal tray is intended to reduce bone–cement implant interface stresses [1–4]. Additionally, the self-aligning nature of the implants has been promoted as to simplify the surgical procedures and increase the margin for error, although the surgery involved requires perfect soft tissue balancing [5]. However, these advantages are theoretical. There have been no clinical studies indicating that mobile-bearing designs provide better longevity or motion than wellfunctioning fixed-bearing knees [2,4,5].
⁎ Corresponding author. Tel.: +81 59 231 5022; fax: +81 59 231 5211. E-mail address: [email protected] (M. Hasegawa). 0968-0160/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2006.07.002
After mobile-bearing TKA, dislocation or spin-out can occur as a result of excessive rotation of the polyethylene bearing accompanied by translation of the femur on the tibia. Because the medial or lateral femoral condyle remains engaged with one side of the bearing, “spin-out” is a more accurate term than dislocation. If a fixed-bearing knee dislocates, both femoral condyles become disengaged; this can occur with a rotating platform, but that is very rare [6]. Here, we describe an unusual complication of dislocation after primary TKA using a posterior-stabilized rotating platform (PFC Sigma RP, DePuy/Johnson & Johnson, Warsaw, IN) with spontaneous reduction. 2. Case report A 65-year-old man (height, 160 cm; weight, 70kg) with muscle weakness in both legs due to cervical spondylotic myelopathy presented with painful osteoarthritis of bilateral knees with 15° varus deformity. The varus angulation was passively correctable to 5°. Range of motion of bilateral knees was 0° of extension and 110° of flexion with 10° of
M. Hasegawa et al. / The Knee 13 (2006) 478–482
extension lag. He required two crutches for ambulation. The palsy affected his right leg more than his left. Two years earlier, he had undergone laminoplasty of the cervical spine. The present procedure was a right TKA using a posteriorstabilized mobile-bearing prosthesis (PFC Sigma RP, DePuy/ Johnson & Johnson). The components were fixed with cement. The tibial component was a highly polished, 4.8mm-thick, cobalt–chromium alloy baseplate with nearly full conformity in the coronal and sagittal planes. The polyethylene insert of the posterior-stabilized version includes a central cone that engages a matching conical cavity in the tibial tray, and includes a 16-mm post to protect against bearing dislocation. This device permits unconstrained axial rotation, minimizing shear stress at the tibial tray bone– cement interface [2]. The medial release was done in steps by first removing medial osteophytes and raising deep and superficial medial collateral ligaments from the upper medial aspect of the tibia. The semimembranosus and posterior capsule were then released. The posterior cruciate ligament was excised. During the operation, ligament balance was found to be acceptable, although varus stress instability was greater than valgus stress instability in both flexion and extension. Flexion gap was greater than extension gap, however, the difference was within 2 mm.
479
The patient was allowed full weight bearing 2 days postoperatively. He quickly achieved 120° of flexion, but he could not stand on his right leg because of palsy. On postoperative day four, his right knee showed severe swelling without pain, and the flexion angle was restricted to 90°. Radiographs revealed dislocation of the polyethylene insert (Fig. 1). Both lateral and medial sides of the rotating platform were dislocated, as shown in Fig. 2. The dislocation could not be reduced by closed manipulation, and we decided to perform open reduction 1 week later with contralateral TKA. However, 6days after the dislocation, the swelling decreased and the patient again achieved 120° of flexion. Radiography revealed spontaneous reduction of the polyethylene insert (Figs. 3 and 4). Varus and valgus stress tests of the knee were performed at extension using a Teros arthrometer (Fa Telos, Medizinisch-Technische Griesheim, Germany), applying 150 N immediately above the joint on the lateral or medial femoral condyle. Radiographs were taken after the force had been applied for 1min. The laxity for valgus stress was 6°, and the angle for varus stress was 10°. Twenty-twomonths postoperatively, the patient reported no pain with a range of motion from 0° to 130°. Presently, the patient is independently ambulatory with double crutches
Fig. 1. Radiographs of the right knee 4days postoperatively demonstrating dislocation of the rotating platform. (A) Anteroposterior radiograph showed symmetry of the joint space between the femoral and tibial components. (B) Lateral radiograph showed radiolucent image of the dislocated polyethylene insert with complete disengagement of both condyles.
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M. Hasegawa et al. / The Knee 13 (2006) 478–482
Fig. 2. Photographs of PFC Sigma RP showing 90° of axial rotation of polyethylene insert disengaged from both the medial and lateral condyles. Saw bone model demonstrating dislocation of posterior stabilized mobile-bearing knee prosthesis (A: frontal view, B: lateral view).
Fig. 3. Radiographs of the right knee 6days after the dislocation demonstrating spontaneous reduction of the dislocation. Both anteroposterior radiograph (A) and lateral radiograph (B) showing satisfactory alignment.
M. Hasegawa et al. / The Knee 13 (2006) 478–482
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Fig. 4. Photographs of PFC Sigma RP after spontaneous reduction. Saw bone model demonstrating reduction (A: frontal view, B: lateral view).
(limited by weakness of leg muscles). Although the patient has not been immobilized, bearing dislocation has not recurred. The coronal laxity showed 6° for both valgus and varus stress. The knee remained to have great laxity, however, varus– valgus balance was obtained without further procedure. 3. Discussion There have been several reports of dislocation after TKA using a mobile-bearing prosthesis [5–10]. Although bearing dislocation is an unusual complication, it is the most important potential early complication of mobile-bearing TKA. The reported incidence of polyethylene dislocation has ranged from 0% to 9.3% [2–4,7,9]. In contrast, fixed-bearing posterior-stabilized knee arthroplasty has a very low reported incidence of dislocation, ranging from 0% to 0.5% [11–13]. In most reported series of mobile-bearing polyethylene TKA, dislocation most often occurred in the early postoperative period, and was attributed to technical failure rather than prosthesis design [7,10]. Thompson et al. [9] reported 10patients with rotating-platform dislocation after primary TKA using LCS, from a series of 2485 patients. All dislocations occurred between 6 days and 2 years after the index arthroplasty. With the asymptomatic patients, the precise time the dislocation occurred was unknown, and all dislocations were detected on radiographs at the 3- or 6month follow-up. The causes of dislocation after mobilebearing or fixed-bearing knee arthroplasty are multifactorial,
including component malposition, prosthesis design, extensor mechanism dysfunction, hamstring spasm, extensive posterolateral release, and increased flexion laxity [5,6,8– 13]. Many surgeons consider that the severe preoperative deformity, which required extensive soft tissue release, contribute to dislocation or subluxation of mobile-bearing knees [4,9,14]. It is clear that not all patients are candidates for mobile-bearing knees. Severe preoperative knee deformities may be a contraindication to mobile-bearing knees because of the difficulty in ligament balancing and the requirement for extensive soft tissue release, however, the degree of deformity that can be treated mobile-bearing knees is unclear [14]. Extensor mechanism malfunction may permit unopposed pull of the hamstrings, predisposing to posterior dislocation [11]. Weale et al. [15] evaluated in vitro resistance to dislocation of mobile bearing TKA (The Oxford Total Meniscal Knee) using cadaver knees. In the presence of a quadriceps load, dislocation could not be produced. In the absence of a quadriceps load, an anteriorly directed force produced dislocation in 95 of the 300 tests. All but one of the dislocations were unicompartmental (spin-out). The likelihood of dislocation increased during knee flexion. Some reports have recommended approximately 4° of coronal laxity during extension for a LCS mobile-bearing prosthesis [16]. Coronal laxity at flexion is a key factor in reducing the risk of subluxation and dislocation of bearings. Matsuda et al. [17] measured laxity with the knee flexed 75°, and recommended 3° of laxity.
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M. Hasegawa et al. / The Knee 13 (2006) 478–482
Dislocation of posterior-stabilized fixed knee arthroplasty is very rare. To our knowledge, the present case is the first reported dislocation after primary knee arthroplasty with a posterior-stabilized rotating platform. In the present case, one of the causes of dislocation appears to be insufficient extensor mechanism function, as indicated by the myelopathy. Contralateral knee pain and muscle weakness may have contributed to the dislocation, although the lack of ligament balancing was most probably the primary etiology for this dislocation. We believe that soft tissue ligament laxity contributed to dislocation rather than just muscle weakness alone. Spontaneous reduction is unusual after dislocation of knee arthroplasty. If coronal laxity is extremely severe, dislocation can recur. Huang et al. [10] reported spontaneous reduction in patients treated using the LCS system without post-cam mechanism. Mobile bearing might be contraindicated in this low demand patient, where there was a known increased risk of dislocation related to prosthetic design and quadriceps insufficiency. The problem of bearing dislocation has prompted a review of design parameters to evaluate alternative approaches to reducing the already-low incidence of these complications. The addition of a rotational stop pin that allows 90° of axial rotation has helped to eliminate this problem. Introduced in 1991, this important modification virtually eliminated dislocations in a consecutive series of 130 primary and multiply operated knees followed over a 10-year period, without causing loosening or increasing wear [1]. Many mobile-bearing knee designs are commercially available, although LCS (DePuy/Johnson & Johnson) and PFC Sigma RP (DePuy/ Johnson & Johnson) are the only 2 primary rotatingplatform knee implants approved by the U.S. Food and Drug Administration. In the PFC Sigma RP system, rotation of the platform element on the tibial baseplate is unrestricted because the system has no rotation stop mechanism, as in the LCS system. To prevent rotatingplatform dislocation, it has been suggested that a restraint mechanism be used to limit rotation of the polyethylene element on the tibial baseplate [10]. Some of the rotatingplatform designs used in Europe and Japan include such a restraint mechanism [14,18], although the surgical technique requires precise soft tissue balancing and balanced flexion and extension gaps. Mobile-bearing knees should be used with caution in patients with extensor mechanism weakness and fixed deformity requiring extensive soft tissue release.
References [1] Buechel FF. In: Callaghan JJ, Rosenberg AG, Rubash HE, Simonian PT, Wickiewicz TL, editors. Mobile bearing knee replacement. The adult knee. Philadelphia: Lippincott Williams & Wilkins; 2003. p. 1163–76. [2] Ranawat AS, Rossi R, Loreti I, Rasquinha VJ, Rodriquez JA, Ranawat CS. Comparison of the PFC Sigma fixed-bearing and rotating-platform total knee arthroplasty in the same patient: short-term results. J Arthroplast 2004;19:35–9. [3] Callaghan JJ, O'Rourke MR, Iossi MF, Liu SS, Goetz DD, Vitteto DA, et al. Cemented rotating-platform total knee replacement. A concise follow-up, at a minimum of fifteenyears, of a previous report. J Bone Jt Surg, Am Vol 2005;87:1995–8. [4] Bhan S, Malhotra R, Kiran EK, Shukla S, Bijjawara M. A comparison of fixed-bearing and mobile-bearing total knee arthroplasty at a minimum follow-up of 4.5 years. J Bone Jt Surg, Am Vol 2005;87:2290–6. [5] Ridgeway S, Moskal JT. Early instability with mobile-bearing total knee arthroplasty: a series of 25 cases. J Arthroplast 2004;19:686–93. [6] Beverland DE, Jordan LR. In: Hamelynck KJ, Stiehl JB, editors. LCS rotating platform dislocation and spinout – etiology, diagnosis and management. LCS mobile bearing knee arthroplasty. A 25years worldwide review. Berlin: Springer; 2002. p. 235–40. [7] Bert JM. Dislocation/subluxation of meniscal bearing elements after New Jersey low-contact stress total knee arthroplasty. Clin Orthop 1990;254:211–5. [8] Rao V, Targett JP. Instability after total knee replacement with a mobile-bearing prosthesis in a patient with multiple sclerosis. J Bone Jt Surg, Br Vol 2003;85:731–2. [9] Thompson NW, Wilson DS, Cran GW, Beverland DE, Stiehl JB. Dislocation of the rotating platform after low contact stress total knee arthroplasty. Clin Orthop 2004;425:207–11. [10] Huang CH, Ma HM, Liau JJ, Ho FY, Cheng CK. Late dislocation of rotating platform in New Jersey low-contact stress knee prosthesis. Clin Orthop 2002;405:189–94. [11] Insall J, Scott WN, Ranawat CS. The total condylar knee prosthesis. A report of two hundred and twenty cases. J Bone Jt Surg, Am Vol 1979;61:173–80. [12] Gidwani S, Langkamer VG. Recurrent dislocation of a posteriorstabilized prosthesis: a series of three cases. Knee 2001;8:17–320. [13] Lombardi Jr AV, Mallory TH, Vaughn BK, Krugel R, Honkala TK, Sorscher M, et al. Dislocation following primary posterior-stabilized total knee arthroplasty. J Arthroplast 1993; 8:633–9. [14] Vertullo CJ, Easley ME, Scott WN, Insall JN. Mobile bearings in primary knee arthroplasty. J Am Acad Orthop Surg 2001;9:355–64. [15] Weale AE, Feikes J, Prothero D, O'Connor JJ, Murray D, Goodfellow J. In vitro evaluation of the resistance to dislocation of a meniscalbearing total knee prosthesis between 30degrees and 90degrees of knee flexion. J Arthroplast 2002;17:475–83. [16] Matsuda Y, Ishii Y. In vivo laxity of low contact stress mobile-bearing prostheses. Clin Orthop 2004;419:138–43. [17] Matsuda Y, Ishii Y, Noguchi H, Ishii R. Effect of flexion angle on coronal laxity in patients with mobile-bearing total knee arthroplasty prostheses. J Orthop Sci 2005;10:37–41. [18] Wilson CJ, Fitzgerald B, Tait GR. Fiveyear review of the Rotaglide total knee arthroplasty. Knee 2003;10:167–71.
Short Communication
Dislocation of posterior-stabilized mobile-bearing knee prosthesis A case report Masahiro Hasegawa ⁎, Akihiro Sudo, Aki Fukuda, Atsumasa Uchida Department of Orthopaedic Surgery, Mie University Graduate School of Medicine, 2-174 Edobashi, Tsu City, Mie 514-8507, Japan Received 12 June 2006; received in revised form 12 July 2006; accepted 23 July 2006
Abstract Spin-out of mobile-bearing knees is a significant early complication of mobile-bearing total knee arthroplasty. Dislocation of the cam-post mechanism of fixed-bearing posterior-stabilized knees occurs more rarely. We have observed an unusual case of dislocation of posteriorstabilized rotating-platform total knee arthroplasty, which has both a cam-post mechanism and rotating platform. A 65-year-old man with knee osteoarthritis and cervical spondylotic myelopathy underwent total knee arthroplasty using a mobile-bearing prosthesis. The dislocation, which occurred 4 days postoperatively, could not be reduced by closed manipulation. However, spontaneous reduction occurred 6 days after the dislocation, which did not recur. A gap mismatch or trapezoidal-shaped gaps may lead to dislocation or spin-out of the bearing insert. This case illustrates that dislocation of a posterior-stabilized mobile-bearing total knee arthroplasty can occur, and both quadriceps deficiency and ligament laxity may contribute to the risk of dislocation. © 2006 Elsevier B.V. All rights reserved. Keywords: Total knee arthroplasty; Dislocation; Mobile-bearing; Posterior-stabilized; Complication
1. Introduction In mobile-bearing total knee arthroplasty (TKA), congruency between the femoral component and the superior surface of the rotating polyethylene in a mobile-bearing design is intended to reduce polyethylene contact stresses, while rotation between the inferior polyethylene surface and the metal tray is intended to reduce bone–cement implant interface stresses [1–4]. Additionally, the self-aligning nature of the implants has been promoted as to simplify the surgical procedures and increase the margin for error, although the surgery involved requires perfect soft tissue balancing [5]. However, these advantages are theoretical. There have been no clinical studies indicating that mobile-bearing designs provide better longevity or motion than wellfunctioning fixed-bearing knees [2,4,5].
⁎ Corresponding author. Tel.: +81 59 231 5022; fax: +81 59 231 5211. E-mail address: [email protected] (M. Hasegawa). 0968-0160/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2006.07.002
After mobile-bearing TKA, dislocation or spin-out can occur as a result of excessive rotation of the polyethylene bearing accompanied by translation of the femur on the tibia. Because the medial or lateral femoral condyle remains engaged with one side of the bearing, “spin-out” is a more accurate term than dislocation. If a fixed-bearing knee dislocates, both femoral condyles become disengaged; this can occur with a rotating platform, but that is very rare [6]. Here, we describe an unusual complication of dislocation after primary TKA using a posterior-stabilized rotating platform (PFC Sigma RP, DePuy/Johnson & Johnson, Warsaw, IN) with spontaneous reduction. 2. Case report A 65-year-old man (height, 160 cm; weight, 70kg) with muscle weakness in both legs due to cervical spondylotic myelopathy presented with painful osteoarthritis of bilateral knees with 15° varus deformity. The varus angulation was passively correctable to 5°. Range of motion of bilateral knees was 0° of extension and 110° of flexion with 10° of
M. Hasegawa et al. / The Knee 13 (2006) 478–482
extension lag. He required two crutches for ambulation. The palsy affected his right leg more than his left. Two years earlier, he had undergone laminoplasty of the cervical spine. The present procedure was a right TKA using a posteriorstabilized mobile-bearing prosthesis (PFC Sigma RP, DePuy/ Johnson & Johnson). The components were fixed with cement. The tibial component was a highly polished, 4.8mm-thick, cobalt–chromium alloy baseplate with nearly full conformity in the coronal and sagittal planes. The polyethylene insert of the posterior-stabilized version includes a central cone that engages a matching conical cavity in the tibial tray, and includes a 16-mm post to protect against bearing dislocation. This device permits unconstrained axial rotation, minimizing shear stress at the tibial tray bone– cement interface [2]. The medial release was done in steps by first removing medial osteophytes and raising deep and superficial medial collateral ligaments from the upper medial aspect of the tibia. The semimembranosus and posterior capsule were then released. The posterior cruciate ligament was excised. During the operation, ligament balance was found to be acceptable, although varus stress instability was greater than valgus stress instability in both flexion and extension. Flexion gap was greater than extension gap, however, the difference was within 2 mm.
479
The patient was allowed full weight bearing 2 days postoperatively. He quickly achieved 120° of flexion, but he could not stand on his right leg because of palsy. On postoperative day four, his right knee showed severe swelling without pain, and the flexion angle was restricted to 90°. Radiographs revealed dislocation of the polyethylene insert (Fig. 1). Both lateral and medial sides of the rotating platform were dislocated, as shown in Fig. 2. The dislocation could not be reduced by closed manipulation, and we decided to perform open reduction 1 week later with contralateral TKA. However, 6days after the dislocation, the swelling decreased and the patient again achieved 120° of flexion. Radiography revealed spontaneous reduction of the polyethylene insert (Figs. 3 and 4). Varus and valgus stress tests of the knee were performed at extension using a Teros arthrometer (Fa Telos, Medizinisch-Technische Griesheim, Germany), applying 150 N immediately above the joint on the lateral or medial femoral condyle. Radiographs were taken after the force had been applied for 1min. The laxity for valgus stress was 6°, and the angle for varus stress was 10°. Twenty-twomonths postoperatively, the patient reported no pain with a range of motion from 0° to 130°. Presently, the patient is independently ambulatory with double crutches
Fig. 1. Radiographs of the right knee 4days postoperatively demonstrating dislocation of the rotating platform. (A) Anteroposterior radiograph showed symmetry of the joint space between the femoral and tibial components. (B) Lateral radiograph showed radiolucent image of the dislocated polyethylene insert with complete disengagement of both condyles.
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M. Hasegawa et al. / The Knee 13 (2006) 478–482
Fig. 2. Photographs of PFC Sigma RP showing 90° of axial rotation of polyethylene insert disengaged from both the medial and lateral condyles. Saw bone model demonstrating dislocation of posterior stabilized mobile-bearing knee prosthesis (A: frontal view, B: lateral view).
Fig. 3. Radiographs of the right knee 6days after the dislocation demonstrating spontaneous reduction of the dislocation. Both anteroposterior radiograph (A) and lateral radiograph (B) showing satisfactory alignment.
M. Hasegawa et al. / The Knee 13 (2006) 478–482
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Fig. 4. Photographs of PFC Sigma RP after spontaneous reduction. Saw bone model demonstrating reduction (A: frontal view, B: lateral view).
(limited by weakness of leg muscles). Although the patient has not been immobilized, bearing dislocation has not recurred. The coronal laxity showed 6° for both valgus and varus stress. The knee remained to have great laxity, however, varus– valgus balance was obtained without further procedure. 3. Discussion There have been several reports of dislocation after TKA using a mobile-bearing prosthesis [5–10]. Although bearing dislocation is an unusual complication, it is the most important potential early complication of mobile-bearing TKA. The reported incidence of polyethylene dislocation has ranged from 0% to 9.3% [2–4,7,9]. In contrast, fixed-bearing posterior-stabilized knee arthroplasty has a very low reported incidence of dislocation, ranging from 0% to 0.5% [11–13]. In most reported series of mobile-bearing polyethylene TKA, dislocation most often occurred in the early postoperative period, and was attributed to technical failure rather than prosthesis design [7,10]. Thompson et al. [9] reported 10patients with rotating-platform dislocation after primary TKA using LCS, from a series of 2485 patients. All dislocations occurred between 6 days and 2 years after the index arthroplasty. With the asymptomatic patients, the precise time the dislocation occurred was unknown, and all dislocations were detected on radiographs at the 3- or 6month follow-up. The causes of dislocation after mobilebearing or fixed-bearing knee arthroplasty are multifactorial,
including component malposition, prosthesis design, extensor mechanism dysfunction, hamstring spasm, extensive posterolateral release, and increased flexion laxity [5,6,8– 13]. Many surgeons consider that the severe preoperative deformity, which required extensive soft tissue release, contribute to dislocation or subluxation of mobile-bearing knees [4,9,14]. It is clear that not all patients are candidates for mobile-bearing knees. Severe preoperative knee deformities may be a contraindication to mobile-bearing knees because of the difficulty in ligament balancing and the requirement for extensive soft tissue release, however, the degree of deformity that can be treated mobile-bearing knees is unclear [14]. Extensor mechanism malfunction may permit unopposed pull of the hamstrings, predisposing to posterior dislocation [11]. Weale et al. [15] evaluated in vitro resistance to dislocation of mobile bearing TKA (The Oxford Total Meniscal Knee) using cadaver knees. In the presence of a quadriceps load, dislocation could not be produced. In the absence of a quadriceps load, an anteriorly directed force produced dislocation in 95 of the 300 tests. All but one of the dislocations were unicompartmental (spin-out). The likelihood of dislocation increased during knee flexion. Some reports have recommended approximately 4° of coronal laxity during extension for a LCS mobile-bearing prosthesis [16]. Coronal laxity at flexion is a key factor in reducing the risk of subluxation and dislocation of bearings. Matsuda et al. [17] measured laxity with the knee flexed 75°, and recommended 3° of laxity.
482
M. Hasegawa et al. / The Knee 13 (2006) 478–482
Dislocation of posterior-stabilized fixed knee arthroplasty is very rare. To our knowledge, the present case is the first reported dislocation after primary knee arthroplasty with a posterior-stabilized rotating platform. In the present case, one of the causes of dislocation appears to be insufficient extensor mechanism function, as indicated by the myelopathy. Contralateral knee pain and muscle weakness may have contributed to the dislocation, although the lack of ligament balancing was most probably the primary etiology for this dislocation. We believe that soft tissue ligament laxity contributed to dislocation rather than just muscle weakness alone. Spontaneous reduction is unusual after dislocation of knee arthroplasty. If coronal laxity is extremely severe, dislocation can recur. Huang et al. [10] reported spontaneous reduction in patients treated using the LCS system without post-cam mechanism. Mobile bearing might be contraindicated in this low demand patient, where there was a known increased risk of dislocation related to prosthetic design and quadriceps insufficiency. The problem of bearing dislocation has prompted a review of design parameters to evaluate alternative approaches to reducing the already-low incidence of these complications. The addition of a rotational stop pin that allows 90° of axial rotation has helped to eliminate this problem. Introduced in 1991, this important modification virtually eliminated dislocations in a consecutive series of 130 primary and multiply operated knees followed over a 10-year period, without causing loosening or increasing wear [1]. Many mobile-bearing knee designs are commercially available, although LCS (DePuy/Johnson & Johnson) and PFC Sigma RP (DePuy/ Johnson & Johnson) are the only 2 primary rotatingplatform knee implants approved by the U.S. Food and Drug Administration. In the PFC Sigma RP system, rotation of the platform element on the tibial baseplate is unrestricted because the system has no rotation stop mechanism, as in the LCS system. To prevent rotatingplatform dislocation, it has been suggested that a restraint mechanism be used to limit rotation of the polyethylene element on the tibial baseplate [10]. Some of the rotatingplatform designs used in Europe and Japan include such a restraint mechanism [14,18], although the surgical technique requires precise soft tissue balancing and balanced flexion and extension gaps. Mobile-bearing knees should be used with caution in patients with extensor mechanism weakness and fixed deformity requiring extensive soft tissue release.
References [1] Buechel FF. In: Callaghan JJ, Rosenberg AG, Rubash HE, Simonian PT, Wickiewicz TL, editors. Mobile bearing knee replacement. The adult knee. Philadelphia: Lippincott Williams & Wilkins; 2003. p. 1163–76. [2] Ranawat AS, Rossi R, Loreti I, Rasquinha VJ, Rodriquez JA, Ranawat CS. Comparison of the PFC Sigma fixed-bearing and rotating-platform total knee arthroplasty in the same patient: short-term results. J Arthroplast 2004;19:35–9. [3] Callaghan JJ, O'Rourke MR, Iossi MF, Liu SS, Goetz DD, Vitteto DA, et al. Cemented rotating-platform total knee replacement. A concise follow-up, at a minimum of fifteenyears, of a previous report. J Bone Jt Surg, Am Vol 2005;87:1995–8. [4] Bhan S, Malhotra R, Kiran EK, Shukla S, Bijjawara M. A comparison of fixed-bearing and mobile-bearing total knee arthroplasty at a minimum follow-up of 4.5 years. J Bone Jt Surg, Am Vol 2005;87:2290–6. [5] Ridgeway S, Moskal JT. Early instability with mobile-bearing total knee arthroplasty: a series of 25 cases. J Arthroplast 2004;19:686–93. [6] Beverland DE, Jordan LR. In: Hamelynck KJ, Stiehl JB, editors. LCS rotating platform dislocation and spinout – etiology, diagnosis and management. LCS mobile bearing knee arthroplasty. A 25years worldwide review. Berlin: Springer; 2002. p. 235–40. [7] Bert JM. Dislocation/subluxation of meniscal bearing elements after New Jersey low-contact stress total knee arthroplasty. Clin Orthop 1990;254:211–5. [8] Rao V, Targett JP. Instability after total knee replacement with a mobile-bearing prosthesis in a patient with multiple sclerosis. J Bone Jt Surg, Br Vol 2003;85:731–2. [9] Thompson NW, Wilson DS, Cran GW, Beverland DE, Stiehl JB. Dislocation of the rotating platform after low contact stress total knee arthroplasty. Clin Orthop 2004;425:207–11. [10] Huang CH, Ma HM, Liau JJ, Ho FY, Cheng CK. Late dislocation of rotating platform in New Jersey low-contact stress knee prosthesis. Clin Orthop 2002;405:189–94. [11] Insall J, Scott WN, Ranawat CS. The total condylar knee prosthesis. A report of two hundred and twenty cases. J Bone Jt Surg, Am Vol 1979;61:173–80. [12] Gidwani S, Langkamer VG. Recurrent dislocation of a posteriorstabilized prosthesis: a series of three cases. Knee 2001;8:17–320. [13] Lombardi Jr AV, Mallory TH, Vaughn BK, Krugel R, Honkala TK, Sorscher M, et al. Dislocation following primary posterior-stabilized total knee arthroplasty. J Arthroplast 1993; 8:633–9. [14] Vertullo CJ, Easley ME, Scott WN, Insall JN. Mobile bearings in primary knee arthroplasty. J Am Acad Orthop Surg 2001;9:355–64. [15] Weale AE, Feikes J, Prothero D, O'Connor JJ, Murray D, Goodfellow J. In vitro evaluation of the resistance to dislocation of a meniscalbearing total knee prosthesis between 30degrees and 90degrees of knee flexion. J Arthroplast 2002;17:475–83. [16] Matsuda Y, Ishii Y. In vivo laxity of low contact stress mobile-bearing prostheses. Clin Orthop 2004;419:138–43. [17] Matsuda Y, Ishii Y, Noguchi H, Ishii R. Effect of flexion angle on coronal laxity in patients with mobile-bearing total knee arthroplasty prostheses. J Orthop Sci 2005;10:37–41. [18] Wilson CJ, Fitzgerald B, Tait GR. Fiveyear review of the Rotaglide total knee arthroplasty. Knee 2003;10:167–71.