International Orthopaedics (SICOT) DOI 10.1007/s00264-014-2564-y
ORIGINAL PAPER
Clinical results of unicompartmental arthroplasty for knee osteoarthritis using a tibial component with screw fixation Tomihisa Koshino & Koji Sato & Yusuke Umemoto & Yasushi Akamatsu & Ken Kumagai & Tomoyuki Saito
Received: 8 September 2014 / Accepted: 1 October 2014 # SICOT aisbl 2014
Abstract Purpose Unicompartmental knee prostheses with screw fixation into the proximal tibia were employed and postoperative clinical results for osteoarthritis of the knee, especially regarding relief of pain, range of motion and satisfactory limb alignment are reported and discussed. Methods A total of 140 knees (131 medial and 9 lateral) of 85 patients (21 men and 64 women) were followed up for two to 17 years with an average of 7.0±3.0 years. Results In spite of loss to follow-up in three knees of two patients and revision to total knee arthroplasty in one knee of one patient, in the remaining 136 knees (82 patients) the mean knee score of the Knee Society Clinical Rating System was 41.0±14.7 pre-operatively, which improved to 93.1±5.7 at follow-up, while the mean functional score similarly improved from 36.9±8.1 to 88.5±6.3 (p<0.001 respectively). One knee developed a fracture in the medial proximal part of the tibia, but no knee developed loosening of the prosthesis or infection. The mean pre-operative knee flexion was 122.6±15.9°, which improved to 132.9 ± 13.4° (p < 0.001) at follow-up. The limb alignment showed 4.8±4.5° anatomical varus angulation pre-operatively, which was corrected to 5.8±3.3° valgus at followup in the medial unicompartmental replacement group (127 knees), and 19±6.1° valgus pre-operatively, which was corrected to 6.7 ± 3.0° valgus at follow-up in the lateral unicompartmental replacement group (nine knees). Conclusions The clinical results of arthroplasty with screw fixation were concluded to be promising.
Keywords Unicompartmental knee arthroplasty . Knee osteoarthritis . Tibial component with screw fixation . High knee flexion . Importance of postoperative limb alignment
Introduction In the medial compartmental osteoarthritic (OA) knee, bone and cartilage degeneration is localised to the medial compartment, and thus single compartmental arthroplasty is a suitable procedure as well as high tibial osteotomy. Formerly, several authors reported poor results with unicompartmental knee arthroplasty (UKA) [1–6] in which failure may have been due to unstable fixation of the implants or to complicated surgical techniques. The causes of failure were considered to be articular cartilage degeneration of the opposite healthy compartment by infiltration of polyethylene debris and particles of bone cement used for fixation [7–9]. The postoperative malalignment of the limb may accelerate loosening and migration of the prosthesis [9, 10]. UKA may have several advantages: (1) minimal bone resection, (nearly one third of total knee replacement), (2) minimal dissection of soft tissue and (3) maintenance of normal knee function and kinematics, and better clinical results were reported [9, 11–13]. In this study, the follow-up results obtained with the “Uni Compartment Knee” (Nakashima Medical Co., Ltd., Okayama, Japan) using a tibial component with screw fixation (Fig. 1) are reported.
Patients and methods T. Koshino (*) : K. Sato : Y. Umemoto : Y. Akamatsu : K. Kumagai : T. Saito Orthopaedic Surgery, Yokohama City University School of Medicine, Yokohama, Japan e-mail:
[email protected]
Patients From 1995, at the Kohga Community Hospital of Yaizu City and at Yokohama City University Hospitals in Japan, 140
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Fig. 1 Schema of lateral view of Uni Compartment Knee. Femoral component (a), tibial component (b), drill hole for a screw and a reverse rounded nut (c), polyethylene (UHMWPE) plate (d) and screw with length 20–80 mm with 5-mm increments (e)
primary OA knees of 85 patients (34 knees of 21 men and 106 knees of 64 women ) underwent UKA using a Uni Compartment Knee (Fig. 1). Of the patients, 55 (110 knees) underwent UKA bilaterally and 30 (30 knees) unilaterally (Table 1). The follow-up period ranged from two to 17 years
(mean 7.0±3.0). The age of the patients at operation ranged from 66 to 86 years with a mean of 75.5±4.8 years (men 75.1 ±5.0, range 63 to 86; women 75.8±4.8, range 66 to 86) (Table 2). Seventy-nine patients were more than 70 years of age. The diagnosis was medial compartmental OA in 131 knees of 79 patients treated with medial replacement, while it was lateral compartmental OA in nine knees of six patients with lateral replacement. Among 55 patients with bilateral knee replacements, two cases had lateral replacement in the right knee and medial replacement in the left. In this series, UKA was indicated for the knees with unicompartmental OA in which the severity of OA evaluated in the one-leg standing radiograph with a grading system [8] modified from Ahlbäck’s classification [14] showed that all knees were categorised as grade 3 or more (Tables 2 and 3). Further, all knees with medial compartmental OA in this series showed slight valgus angulation and normal thickness of the lateral joint space by valgus force exerted on the knee, which means the limb alignment can be corrected by valgus force.
Table 1 Total cases of surgeries using the Uni Compartment Knee
M:male, F:female, p:patient, k:knee *Among them, 4 knees (3 patients) underwent UKA after high tibial osteotomy, and 3 knees (3 patients) had secondary OA (2 knees with osteonecrosis and one after infectious arthritis)
International Orthopaedics (SICOT) Table 2 Demographic data (total analysed)
Table 3 Range of motion, knee score and alignment 1
Knee ROM Flexion deformity (flexion contracture) Max. knee flexion Knee Society Clinical Rating System Knee score Functional score
2
3
Limb alignment (standing femorotibial angle) Medial UKA Lateral UKA
ROM range of motion *p<0.01; **p<0.001 a
4.8° anatomical varus angulation
b
3° valgus to 17° varus
c
5.8° valgus
d
20° valgus to 4° varus
e
9° valgus
f
10–16° valgus
g
6.7° valgus
h
4–13° valgus
N 127 knees 9 knees
Preoperative (range) 10.6±7.4° (0–30°) 122.6±15.9° (70–150°)
Postoperative (range) 1.7±3.6° (0–15°)* 132.7±13.4° (80–150°)**
41.6±14.7 (10–70) 36.9±8.2 (25–10)
93.1±5.7 (75–100)** 88.5±6.3 (65–100)**
184.8±4.4°a (177–197°)b 161.0±6.1°e (154–170°)f
174.2±3.3°c (160–184°)d** 173.3±3.0°g (167–176°)h**
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UKA with screw fixation of tibial component The tibial component model has been changed to have more stability after insertion into the tibial condyle. The Marmortype tibial component, just like a plain plate, and several prostheses developed later had small stems or a short fin underneath the tibial plate for a stopper. But in the mobilebearing prostheses, however, a mobile component may be easily dislocated by deep (more than 130°) knee flexion. This Uni Compartment Knee (Fig. 1) has the tibial component with two long screws underneath for fixation to the tibial condyle which may prevent the implants from dislocation of the component and from tibial condylar fractures, and each of those screws is prevented from coming out by insertion of a reverse rounded nut on the top of it. The tibial component of the Uni Compartment Knee is of a fixed insert with flat surface. Operative techniques of unicompartmental knee replacement with screw fixation A central, longitudinal, slightly laterally curved skin incision of 10 cm is made on the anterior aspect of the knee (over the medial part of the patella), from a point 2 cm above the patella, to a point 1 cm medial to the tibial tuberosity. The underlying investing layer is then divided along the skin incision line. The retinaculum and capsule are divided along the medial side of the patellar ligament and patella. On the medial side of the proximal end of the tibia, the periosteum is divided longitudinally and elevated, and the insertion of the medial collateral ligament is elevated subperiosteally together with the insertion of the pes anserinus (medial extensive subperiosteal release). Especially for the knee with flexion contracture more than 15°, more extensive medial subperiosteal release is necessary. Proximally, the incision is extended upward along the medial edge of the patella, ending in the subvastus approach. The capsule is divided longitudinally up to the suprapatellar pouch to open the joint and expose the medial femoral condyle. For a patient whose postoperative knee flexion is to be enhanced more, a longitudinal lateral release of the retinaculum and capsule is performed along the lateral side of the patellar ligament and the patella, and then between the rectus and the vastus lateralis. Under a full extension of the knee, the most anterior edge of the medial tibial plateau is marked on the articular surface of the corresponding medial femoral condyle, which is line A (Fig. 2a), the fundamental line of the femoral component setting (positioning). At 90° knee flexion, the femoral component template is applied with its anterior edge on line A, and the posterior portion of the medial femoral condyle is osteotomised 45° obliquely downward at the posterior end of the template. Subsequently, a tibial cutting guide is applied along the tibia and adjusted for the horizontal cut in the medial
tibial plateau perpendicular to the shaft of the tibia with a 5° posterior slope. Minimum bone resection is performed at the medial tibial plateau vertically along the line just medial to the central eminentia and horizontally. At the resected surface the template of the tibial component is fixed with two nails. Two holes are drilled in the resected surface along the holes of the tibial template (Fig. 2b). A tibial trial is placed on the resected surface for adjustment. Subsequently, the femoral template is applied and fixed with pins at the articular surface of the medial femoral condyle with its anterior edge on line A. Two drill holes are made for the femoral component stems (Fig. 2a). Then, the femoral and tibial components (trials) are inserted, and the limb alignment is checked to select the thickness of the tibial polyethylene plate. The ideal postoperative limb alignment should be aimed to be of 8° of anatomical valgus angulation (172° femorotibial angle, FTA [8, 9, 15]) in standing, in which the mechanical axis of the lower extremity passes through the centre of the knee [25]. Small anchoring holes are made in the tibial surface, on which the tibial component is fixed firmly with bone cement and two screws. The femoral component is fixed with bone cement. An ultrahigh molecular weight polyethylene (UHMWPE) plate of appropriate size and thickness is then inserted into the upper surface of the tibial component. The subcutaneous tissue (investing layer) and the skin are closed in maximum flexion. Simultaneous bilateral (left and right) UKA was performed in 38 knees of 19 patients among the total of 140. Postoperative management On the first postoperative day, the patient is instructed to do active knee range of motion (ROM) exercises by dangling the leg and with a continuous passive motion (CPM) machine but no passive motion exercise by physiotherapists and is encouraged to do straight leg raise exercises for quadriceps strengthening. Partial or full weight-bearing is permitted as tolerated under the guidance of physical therapy on the first or second day. All patients were checked preoperatively and followed up directly postoperatively using special check sheets, and anteroposterior and lateral one-leg standing radiographs were taken (Fig. 3a, b).
Results Survivorship and loosening Kaplan-Meier survivorship curves with corresponding 95 % confidence intervals were calculated with failure defined according to two end points: (1) revision by total knee arthroplasty (one patient with one knee in this series) and (2) moderate pain remaining at the final follow-up at two years or
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Fig. 2 Surgical procedures. a A 10-cm anterior laterally curved longitudinal skin incision and subvastus approach to open the knee together with a long longitudinal lateral release of the retinaculum and capsule. With the knee in complete extension, line A is marked out at the most anterior edge of the tibial plateau. Drilling (B) is performed for the stems of the femoral component. At 90° knee flexion, the femoral cutting guide (C) is applied
with its anterior end adjusted at line A. Two drill holes are made for the anchoring stems. The femoral trial (D) is applied for testing. b The tibial template is placed on the osteotomised surface of the tibial plateau and two drill holes are made for fixation. The tibial component is fixed on the tibial plateau with bone cement and two screws
more after UKA (no patient with no knee in this series). Data are expressed as mean±standard deviation. Clinical and radiographic data were compared between pre- and postoperative findings. The unpaired two-tailed t test was used for statistical analysis. Values of p<0.05 were considered statistically significant. Excluding three patients (five knees) who died, the probability of the knee remaining free of failure (revision) was calculated at the final follow-up. No case of loosening was experienced in this series. In the worst-case scenario in which loss to follow-up before ten years was regarded as failure (no cases in this series), the figures for survivorship were 98.7 % at five years and 93.4 % at ten years.
and the functional score from 36.9±8.2 pre-operatively to 88.5±6.3 postoperatively (p<0.001). Ten knees of eight patients (all but one knee with medial replacement) with rupture of the anterior cruciate ligament (ACL) found at the time of arthroplasty had knee scores of 87.2±7.1 and functional scores of 83.3±6.6 at the final follow-up, which were significantly a little lower than the averages of this series (p<0.01 and p<0.05 respectively). UKA is indicated even for knee OA with ACL rupture. At the final follow-up, the patients were highly satisfied with the results of UKA in 60 knees, satisfied and stated it was worth recommending in 72 knees and satisfied but stated it was not worth recommending in four knees.
Relief of pain, ROM and knee scores
Limb alignment and patellofemoral OA
The patients were relieved from knee pain and disabilities after surgeries (Fig. 3a–c). Pre-operative walking ability was restricted to less than 300 m because of pain in 70 and to 300– 500 m in 12 of 82 patients, which improved to more than 1,000 m in 76 and to 800–1,000 m in six postoperatively. The knee ROM was expressed from flexion deformity (flexion contracture) to the maximum knee flexion (Table 3). Flexion contracture was improved from 10.6±7.4° (0–30°) pre-operatively to 1.7±3.6° (0–15°) (p<0.01) postoperatively and knee flexion from 122.6±15.9° (70–150°) before to 132.7 ±13.4° (80–150°) (p<0.001) afterwards, and seven patients (eight knees) were able to do formal sitting on the floor, indicating full ROM in this series. The Knee Society Clinical Rating System knee score improved from 41.6± 14.7 pre-operatively to 93.1±5.7 postoperatively (p<0.001)
As to postoperative limb alignment, in the standing anteroposterior radiograph, in 127 knees with medial replacement before surgery, the standing FTA was 184.8±4.4° (4.8° of anatomical varus angulation) (177–197°; 3° valgus to 17° varus), and at the final follow-up it was corrected to 174.2± 3.3° (p<0.001) (6.2° valgus) (160–184°; 20° valgus to 4° varus), while in nine knees with lateral replacement, FTA (standing) was 161.0±6.1° (9.0° valgus) (154–170°, 10 –16° valgus), and at the final follow-up it was corrected to 173.3± 3.0° (p <0.001) (6.7° valgus) (167–176°, 4–13° valgus) (Table 3). There was no knee with a change in component position, radiolucency of 1 mm or more or osteolysis. As to patellofemoral involvement, patellofemoral articulation pain was elicited by grating the patella against the patellar articulation at the distal end of the femur in 77 of 136 knees
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experienced and no dislocation of the tibial component like that of the mobile-bearing system even in deep knee flexion over 140° (Fig. 3c).
Discussion Survivorship and loosening
Fig. 3 Medial compartmental osteoarthritis of right knee of a 74-year-old woman. a Anteroposterior view of right knee in one-leg standing position four years after medial unicompartmental knee replacement. FTA (standing) is measured as 175°. The patient had no pain in the right knee, with a Knee Society rating score of 100 pain points and 95 function points. b Lateral view of Fig. 3a in standing with no flexion contracture. c Lateral view of Fig. 3a with the maximum flexion
before surgery but in only nine knees at the final follow-up. Narrowing in the skyline view of the patellofemoral articulation was pre-operatively observed in 24 knees of this series, which was unchanged at follow-up. Complications There were three knees with breakage of the posterior portion of the femoral component, the prosthesis of which was an older model, two of those cases were replaced with new thicker models and the remaining one knee was revised with total knee replacement. In this series, with 6- to 8-cm long screws for fixation of the tibial component, no fracture was
The remarkable features of UKA in this series were no case with proximal tibial fractures and no case of loosening of the prosthesis, which are interpreted to be due to firmer fixation of the tibial prosthesis to the bone by long screws and to satisfactory postoperative limb alignment. It has been reported that degeneration occurs on the lateral, healthy side after medial unicompartmental replacement [3]. Price and associates [10] reported lateral compartmental degeneration due to valgus alignment after medial Oxford UKA, and Pandit and associates [17] described similar findings due to ACL deficiency, but in this series no patients with medial UKA developed degeneration in the lateral compartment. This is supported by the authors’ previous report on the long-term follow-up results of high tibial osteotomy [15], and further, in this series UKA was performed in primary OA knees of elderly subjects aged more than 70 years. Jonsson [3] reported 17 knees in which degeneration took place on the lateral side among patients who underwent medial replacement, and Marmor observed disappearance of the joint space on the contralateral side in three cases [13]. Laskin [18] observed invasion of small polyethylene debris on the healthy articular surface in a case in which degeneration took place. Koshinen and associates [19] reported wear of the polyethylene liner and progression of OA in the lateral compartment, but their patients were younger and many of the cases in their series died (12 of 54 patients). If the cause of degeneration on the contralateral side is excessive abrasion of polyethylene on the side of the replacement, a more valgus limb alignment should be obtained after medial UKA [20–24] in order to prevent polyethylene abrasion and loosening of the prosthesis. Knee ROM, limb alignment and patellofemoral OA In order to reduce flexion deformity and enhance knee flexion, extensive medial subperiosteal soft tissue release and longitudinal lateral release of the retinaculum and capsule were necessary. In this series, satisfactory knee ROM could be maintained or even improved to some extent. For satisfactory clinical results, the patients should have ideal postoperative limb alignment as in this series and in our previous series [8, 9], similar to those of high tibial osteotomy [15]. As reported previously [25], the mechanical axis passes through the centre of the knee in standing when the FTA is 172° (8° of anatomical valgus angulation), which is an ideal postoperative limb
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alignment to be aimed for in medial unicompartmental replacement. Cartier and associates [11] recommended 0–5° of varus mechanical axis angulation, which was calculated to be an FTA of 172–177°. However, for the valgus-angulated knee (lateral compartment OA of the knee) with an FTA less than 172°, the ideal postoperative limb alignment is an FTA of 172–176° (4–8° anatomical valgus) after lateral compartment replacement. The authors agree that patient selection and good surgical technique [26] are fundamental for prosthesis survival. The UKA (fixed bearing) was reported to be performed even on an outpatient basis [27]. In this series, no cases were found to have developed other compartment degeneration in contrast to opinions of Citak et al. [28] and Mercier et al. [26]. Even the postoperative valgus-angulated knee (overcorrection for medial UKA) was not found to have any symptoms and aggravation in the lateral side. In this series, UKA was concluded to have no bad effect on the status of the patellofemoral joint, contrary to the opinion of Argenson et al. [16].
Acknowledgments The authors wish to express heartfelt appreciation to members and staff in the Department of Orthopaedic Surgery, Yokohama City University School of Medicine, especially Dr. S. Takagawa, for their kind assistance in surgeries. Conflict of interest The authors declare that they have no conflict of interest.
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