Laxitud del mecanismo extensor y luxación posterior atraumática tras artroplastia total de rodilla de revisión. Reporte de caso

Extensor mechanism dysfunction and atraumatic posterior dislocation following revision total knee arthroplasty: a case report

Resumen

Introducción. La luxación de prótesis tras una artroplastia total de rodilla de revisión, aunque rara, es una complicación grave, cuya incidencia viene en aumento debido a que el reemplazo articular es un procedimiento cada vez más frecuente en el manejo de la osteoartritis. Sus principales causas reportadas incluyen inestabilidad en flexión y debilitamiento de los tejidos blandos.

Presentación del caso. Hombre de 79 años con antecedente de revisión de prótesis de rodilla izquierda por aflojamiento séptico, quien en julio de 2024 asistió al servicio de urgencias de una institución de salud de primer nivel de atención de Bogotá (Colombia) por gonalgia izquierda con episodios intermitentes de edema articular y rubor local desde hace 7 meses. Dada la persistencia de los síntomas a pesar del manejo analgésico, fue remitido a una institución de cuarto nivel de atención. La radiografía simple de rodilla izquierda de ingreso mostró patela baja y luxación posterior de prótesis, por lo que se llevó a revisión en dos tiempos quirúrgicos. En el primer tiempo se evidenció laxitud del mecanismo extensor, por lo que en el segundo se aumentó el nivel de constricción con prótesis de bisagra rotacional, obteniéndose adecuada estabilidad articular y restableciéndose el arco de movilidad.

Conclusiones. Los casos de luxación tras artroplastia total de rodilla de revisión son raros, pero pueden presentarse en diversos tipos de implantes, incluyendo los de diseños constreñidos. La laxitud del mecanismo extensor puede contribuir a desencadenar un episodio de luxación posterior crónica que debe tenerse en cuenta durante el planeamiento de una artroplastia total de rodilla de revisión.

Abstract

Introduction: Although prosthesis dislocation after revision total knee arthroplasty is rare, it represents a serious complication, with a rising incidence due to the increasing use of joint replacement for osteoarthritis management. Major reported causes include flexion instability and soft tissue weakening.

Case presentation: A 79-year-old man with a history of left knee revision arthroplasty due to septic loosening presented to the emergency department of a primary care institution in Bogotá (Colombia) in July 2024 with a 7-month history of left knee pain, accompanied by intermittent episodes of joint swelling and local erythema. Given the persistence of symptoms despite analgesic therapy, he was referred to a quaternary care institution. Plain radiographs of the left knee obtained on admission revealed patella baja and posterior dislocation of the prosthesis, leading to a planned two-stage revision procedure. During the first stage, laxity of the extensor mechanism was identified; therefore, during the second stage, the level of constraint was increased using a rotational hinge prosthesis, achieving adequate joint stability and restoration of the range of motion.

Conclusions: Dislocation following revision total knee arthroplasty is rare but can occur in various implant designs, including constrained systems. Laxity of the extensor mechanism may contribute to chronic posterior dislocation and should be carefully considered during preoperative planning for revision total knee arthroplasty.

https://doi.org/10.15446/cr.v11.117740

Keywords: Knee Dislocation; Arthroplasty, Replacement, Knee; Prosthesis Failure

Palabras clave: Luxación de la Rodilla; Artroplastia de Reemplazo de Rodilla; Falla de Prótesis

Camilo Andrés Velandia-Amaya

Jorge Rolando Ortiz-Morales

Universidad Nacional de Colombia - Bogotá Campus -
Faculty of Medicine - Department of Surgery -
Orthopedic and Trauma Surgery Unit -
Bogotá D.C. - Colombia

Corresponding author

Camilo Andrés Velandia-Amaya. Unidad de Ortopedia y Traumatología, Departamento de Cirugía, Facultad de Medicina, Universidad Nacional de Colombia.
Bogotá D.C. Colombia.
Correo electrónico: cavelandiaa@unal.edu.co.

Received: 27/11/2024 Accepted: 11/08/2025

IntroducTIOn

Total knee arthroplasty (TKA) is one of the most successful, cost-effective, and cost-efficient surgeries in orthopedics since it significantly reduces pain, contributes to functional recovery, and, consequently, improves patients’ quality of life (1). Revision TKA is a technically challenging and costly surgical procedure, with results that, despite being good in most cases, are inferior to those obtained with primary TKA, showing a higher failure rate (2).

The number of primary TKAs performed in the last decades has increased considerably, meaning that the number of revision surgeries is also on the
rise (2,3). In fact, it is estimated that between 2005 and 2030, the number of primary TKAs will increase by 174%, while revision TKAs are expected to increase nearly sevenfold (2).

The 10-year survival of a revision implant ranges from 71% to 86% (2,4). According to the literature, between 5% and 50% of patients experience complications (2,5), the most common being persistent joint stiffness and pain, neurovascular problems, extensor mechanism dysfunction, surgical wound complications, and, less frequently, instability (2,5).

In primary TKA, instability remains one of the main reasons for early revision (6). Also, dislocation following this procedure, although rare, is a serious complication (3). The reported incidence of instability and dislocation after primary TKA ranges between 1% and 2% (3), being more frequent in cruciate-retaining designs and decreasing to 0.15-0.5% in newer designs that incorporate modifications in the height of the polyethylene tibial post and its anterior translation (3,7).

Tibiofemoral dislocation is a rare and infrequent complication after
revision TKA, with an incidence of 3.3%, but it is the most severe form of instability after this procedure (8-10). Its specific etiology is unknown, but some of the causes most frequently described in the literature include malposition of the components, imbalance in the flexion and extension space, excessive release of soft tissues, and extensor mechanism laxity, the latter being the least frequently reported (9,10). There is no established protocol for its management, which depends on time since onset, implant characteristics, and patient’s clinical context; however, the most common approach is implant replacement with a more constrained design (3).

The following is the case of a patient with posterior dislocation after
revision TKA. The possible factors associated with the development of this complication are discussed.

Case presentation

In July 2024, a 79-year-old man with a history of high blood pressure, type 2 diabetes mellitus, bilateral TKA (right TKA 14 years ago and left TKA 7 years ago) and revision left TKA with the Columbus® revision system (Aesculap Implant Systems, LLC - B. Braun company) performed 15 months earlier due to septic loosening and an apparent patellofemoral subluxation reported in an extra-institutional surgical report, presented to the emergency department of a primary care health institution in Bogotá (Colombia) due to left gonalgia with intermittent episodes of joint edema and local flushing that began 7 months earlier, which exacerbated when moving and was not associated with any traumatic event. Due to these symptoms, he received treatment with an antistaphylococcal antibiotic one month prior to the consultation and was referred to a tertiary care institution in Bogotá as the symptoms persisted and worsened.

Physical examination on admission revealed left knee in antalgic position (30° flexion) with adequate healing of the surgical wound from the revision TKA performed 15 months earlier, with edema without signs of joint effusion or local infection and with limitation in active range of motion arcs from 30° to 90° due to pain. A body mass index (BMI) of 24.2kg/m2 was calculated.

Admission laboratory tests showed normal levels of leukocytes (6 030mg/dL) and neutrophils (2 640mg/dL), as well as elevated C-reactive protein (CRP) (32mg/L). Plain X-ray of the left knee on admission evidenced patella baja and posterior dislocation of the revision prosthesis (Figure 1). Suspecting a new episode of concomitant periprosthetic infection, blood cultures were taken.

Figure. 1. Plain anteroposterior (AP) and lateral X-ray of the knee. There is evidence of patella baja and posterior dislocation of the revision prosthesis.

Source: Image obtained while conducting the study.

Given the history of septic loosening and anticipating significant bone loss after material removal, the patient was taken to a two-stage revision surgery. First, on July 31, the components were removed, samples were taken for culture, an antibiotic impregnated cement spacer (Gentamicin Knee Spacer Subiton) was implanted, and empirical antibiotic treatment with first-generation cephalosporin was indicated. During the procedure, fibrosis and extensor mechanism hyperlaxity were observed, along with a medial tibial metaphyseal bone defect classified as type IIA according to the AORI classification. The components were in good condition, with no evidence of wear or loosening (Figure 2), and no signs of infection.

Figure. 2. A) Intraoperative photograph taken during the first stage of revision total knee arthroplasty. B) Components removed with no evidence of wear.

Source: Image obtained while conducting the study.

Blood and bone cultures obtained from the femur and tibia after 72 hours of incubation were negative. The patient exhibited no clinical signs of systemic inflammatory response in the immediate postoperative period. Consequently, on August 9, nine days after the initial surgery, the second stage of the revision was performed, and the prosthesis was replaced with a constrained rotating hinge implant (Rotational Knee Joint Prosthesis Endo-Model®, WALDEMAR LINK GmbH & Co., Hamburg). The femoral and tibial components were replaced with cemented M-size implants, and a revision M-size polyethylene insert was implanted. Before completion of the procedure, proper component alignment and stability under varus and valgus stress were confirmed, finding an intraoperative range of motion from 0° to 100°. The immediate postoperative X-ray showed proper component alignment (Figure 3).

Figure 3. A) intraoperative photograph taken during the second stage of revision total knee arthroplasty; B) postoperative anteroposterior and lateral X-rays demonstrating a properly aligned constrained rotating hinge prosthesis.

Source: Image obtained while conducting the study.

The patient was able to maintain limb support and walk with a walker 2 days after surgery. The following rehabilitation protocol was initiated on an outpatient basis: initial phase (day of discharge): passive knee extension, assisted knee flexion–extension using the contralateral lower limb, ankle flexion-extension, and ambulation with walker; phase 2 (from discharge to week 6): active knee
flexion-extension exercises, treadmill ambulation, and stationary cycling; phase 3 (week 7 to 12): active flexion-extension, single-leg balance, proprioceptive training, and stationary cycling; phase 4 (weeks 12–16): ambulation without assistive devices, squatting exercises, and assisted tiptoe walking.

At the 3-month follow-up after the final surgery, the patient reported improvement of symptoms, with a score of 2/10 on the visual analog pain scale, a score of 76/100 (good) on the Knee Society Score, an arc of motion of 0-90° of the left knee, and initiation of ambulation without assistive devices.

Discussion

Prosthesis dislocation following primary TKA is a rare and infrequent complication. However, it should be noted that the number of cases reported in the literature is increasing because joint replacement is becoming a more common procedure for the management of osteoarthritis (11). Dislocations can be classified as posterior or anterior, the latter being the least frequent. Anterior dislocation is mainly associated with cruciate-retaining prostheses, and its etiology involves the combination of ligament instability and increased tibial slope caused by cruciate ligament injury and consequent damage to the medial collateral ligament complex and the patellar tendon (12,13).

On the other hand, posterior dislocation is reported more frequently in patients with posterior stabilized prostheses, and its mechanism seems to be related to the replacement of the posterior cruciate ligament by post-cam and femoral cam models that aim to prevent anterior femoral translation in flexion and recreate physiological femoral recoil (3,14). These models typically provide sufficient jumping distance to avoid dislocation, but posterior dislocation may occur in deep flexion and varus/valgus stress (for which this system does not provide constriction) (3,14,15). Considering the foregoing, it is thought that extensor mechanism dysfunction was the cause of the posterior dislocation in the patient of the present case.

It is worth mentioning that posterior-stabilized knee prostheses (e.g., knee implants with a mobile plate and rotating platform) were specifically designed to provide stability after TKA when the posterior cruciate ligament is deficient or must be sacrificed (16). Complete 180° rotatory dislocation in a mobile plate knee prosthesis is extremely rare. In this regard, Lee et al. (16) published an exceptional case of a complete 180° rotatory dislocation of the rotating platform following a closed reduction of the posterior dislocation of a posterior-stabilized total knee prosthesis. This case demonstrates that dislocation following a posterior-stabilized mobile-bearing TKA can occur given valgus laxity and cause a 90° spin-out of the polyethylene insert, and also that closed reduction attempts may contribute to a complete 180° rotatory dislocation of the rotating platform.

Dislocation after revision TKA is extremely rare and the cases reported in the literature are scarce, including some cases of constrained design implants presenting posterior dislocation (3,17,18), as in our patient, who had a Columbus® revision system implanted in his revision TKA, a system considered to have a constrained design. The cause of dislocation in primary and revision TKA is a matter of debate, but most studies report flexion instability, discrepancy between flexion and extension gaps, multiligament instability, and extensor mechanism failure or insufficiency as triggers (3,19).

In a series of 6 cases of knee dislocation following TKA (2 primary and 4 revision), Kornilov et al. (18) reported extensor mechanism involvement as the cause of dislocation in 4 cases, one of them due to extensor mechanism laxity, as was the case in our patient. Extensor mechanism laxity, as well as chronic injury to the other stabilizing elements of the knee, results from soft tissue weakening, which is often found in knees with multiple previous surgical interventions (20). The subsequent progressive instability is particularly important in extreme flexion ranges as it can trigger a dislocation event when combined with varus and/or
valgus stress (14,15), as occurred in our patient.

The preceding hypothesis is compatible with the findings of Buechel et al. (21),
who in their report of two cases of dislocation after revision TKA suggest that insufficient healing of the soft tissues in a previously operated knee and instability in flexion were the causes of dislocation in these patients. Lee et al. (3),
in their case report of dislocation in a LEGION revision system, also demonstrated that extensor mechanism laxity caused by multiple surgeries for lateral patellofemoral subluxation and musculoskeletal infection can contribute
to dislocation.

Flexion stability is the most frequently associated factor with dislocation events after primary and revision TKA (22,23). In this regard, Abdel et al. (24) identified factors visible on plain X-ray that may contribute to flexion instability after TKA, including decreased condylar displacement, distalization of the joint line, and increased posterior tibial slope.

Treatment in cases of dislocation after primary TKA consists initially of reduction maneuvers through passive extension, traction and immobilization, and its success depends on achieving stability after reduction and adequate rehabilitation through muscle strengthening (3,23). When a stable reduction is not obtained, revision surgery must be performed (25). Replacement of the polyethylene insert with a larger size is sufficient in most patients; however, if there is evidence of severe laxity, gap difference in flexion/extension, or malposition of the components, revision with a prosthesis with a greater degree of constriction is recommended (3,26).

It has been reported that in cases of chronic dislocation after revision TKA, as in the present case, or in whom a larger insert is sufficient (27), few patients are able to achieve a stable closed reduction; in most cases, revision surgery must be performed to increase the level of constriction. In the case reported by Lee et al. (3), revision surgery to increase the size of the polyethylene insert increased stability but did not resolve the pre-existing impingement between the insert and the patella, so the patient required flexion restriction postoperatively.

The presented case describes a chronic dislocation in a patient with a history of revision TKA due to septic loosening and evidence of extensor mechanism laxity, who underwent a first surgical stage for culture collection and application of cement spacer impregnated with antibiotics, and a second stage in which a rotating hinge implant was placed, providing a higher level of constriction that yielded good results. Importantly, in this case it was not possible to ascertain that extensor mechanism laxity was the only triggering factor for dislocation, so larger series are required to establish confounding factors and determine the real impact of an insufficient extensor mechanism.

Conclusions

Cases of dislocation after revision TKA are rare, but can occur with various types of implants, including those of constrained design. The etiology, although unknown, seems to be related to the weakness of the stabilizing soft tissues in patients who have undergone multiple surgeries, which, together with flexion instability, facilitates a subsequent episode of dislocation. This case suggests that extensor mechanism laxity may be an additional factor that can contribute to triggering a chronic posterior dislocation episode and that it should be taken into account during the planning of a revision TKA in order to opt for constrained systems, such as a rotating hinge prosthesis.

Ethical considerations

Only one case is reported and the patient consented to its publication and to the use of images.

Conflicts of interest

None stated by the authors.

Funding

None stated by the authors.

Acknowledgments

None stated by the authors.

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