Introduction

Primary total knee arthroplasty (TKA) is a very successful procedure in orthopedic surgery. Excellent mid- and long-term results have been described [15, 23]. However, not all patients have a successful result. About 10–15% of patients were dissatisfied with the replaced knee [5, 21]. A rate of revisions of about 3% done in the first year after the primary TKA has been reported [9, 24]. Besides infections, these early revisions were done due to mechanical failures mainly. In a retrospective study, 50% of 212 early revisions within 2 years were related to instability, malalignment, failure of fixation and malposition of the tibial and/or femoral component [29].

Combined internal malrotation of tibial and femoral components has been linked to patellofemoral complications [3] and anterior knee pain [2]. Isolated internal femoral component malrotation was a common finding in patients with anterior knee pain [4, 26]. Different symptoms, instability [10, 11, 16, 27] and stiffness [4, 10, 11, 16] with and without good range of motion (ROM) have been reported in these patients. However, the amount of internal malrotation of the femoral component and the clinical significance are still controversial.

Clinical and functional improvement after early revision within 2 years for tibial and/or femoral component malrotation in 22 TKA has been reported recently [11]. In this series, 18 patients needed condylar-constrained and two patients a rotating-hinge design [11]. Another study also showed an improvement in the clinical results after early revision for combined internal malrotated TKA [16].

In the present study, physical examination with specific tests, stress radiographs [30] and computed tomography (CT) [3] were used to evaluate the malrotation of the components in a series of patients with painful TKA. Patients with failed conservative treatment and isolated femoral component malrotation underwent full exchange revision surgery. The hypothesis was that patient would benefit from the revision surgery. The following specific questions were addressed: Are there specific symptoms in patients with isolated internal malrotation of the femoral component at the time of revision? Is there a specific amount of internal malrotation of the femoral component leading to revision surgery? How much constrained is necessary for revision TKA in these cases? Can the correction of isolated internal malrotation of the femoral component improve the clinical and functional outcomes?

Materials and methods

Seventy-two consecutive patients with painful TKA were evaluated in our institute with CT scans to verify the rotational alignment of the femoral and tibial component during the period of 1999 and 2004. We identified 59 patients with rotational malalignment of the tibial and/or femoral component. For this study, patient selection was based on the presence of isolated internal malrotation of the femoral component with no further malalignments or complications. Therefore, 19 patients with isolated tibial and 17 patients with combined tibial and femoral rotational malalignment as well as six patients with isolated femoral component malrotation and frontal malalignment (mechanical alignment outside the range of 3° varus to 3° valgus) were excluded. Two patients with mild internal femoral component malrotation ≤3° were treated conservatively only and excluded also (Table 1).

Table 1 Results in 16 patients in the CT scans, patellar maltracking and treatment

Fourteen patients [8 women, 6 men, mean age of 64 years (SD 10, 41–73 years)] with isolated internal femoral component malrotation ≥4° were left and underwent revision surgery with complete replacement of the tibial and femoral components (Table 1). The revision surgery was done within 36 months (12–36 months) of the primary arthroplasty. All patients had failed conservative treatment for at least 1 year before surgery. No patients were lost to follow-up. The mean follow-up period was 57 months (SD 12, 46–89 months).

For all patients, the primary surgery records were available. The history of pain was explored for quality, location, duration and exacerbation with activity. The patients were asked about pain and problems when walking even with the ground, climbing stairs and rising up from a chair. Symptoms of painful giveaway and patellar dislocation were recorded. Clinical testing included standardized climbing stairs and rising up from a chair and physical examination of passive and active range of motion. A varus and valgus stress test in full extension, 20 and 90° or maximal flexion as well as an anterior drawer test was performed. The tightness or instability of the medial and lateral sides was graded semi-quantitatively. Exclusion of infection for all patients was performed by negative laboratory tests (C-reactive protein and erythrocyte sedimentation rate), joint aspiration and bacterial samples during surgery with prolonged incubation for a minimum of 10 days [7].

Anteroposterior and lateral views, tangential and long leg standing radiographs before and after the operation were performed in all patients. Frontal mechanical full leg alignment measurements on the long leg standing radiographs included the measurements of the mechanical femur and tibia axis, lateral distal femur angle (LDFA) and medial proximal tibia angle (MPTA) [22]. Radiographic assessment of patellar tracking (tilt and subluxation) was made on standardized tangential views [8]. The patellar tilt was defined as the angle between the tangential line of the femoral condyles and the line through the prosthesis bone interface. Values of 5° or less were defined as normal. Abnormal patellar subluxation was defined by the congruence angle more than 16° [20]. Standardized fluoroscopically assisted varus–valgus stress radiographs in 20 and 90° flexion were used for investigation of extension and flexion gap stability [30]. These radiographs were performed with the patient lying on a radiolucent board the knee joint flexed to 20 and 90° [26, 30]. With a handheld spring scale, a standardized force of 15 N to the tibia [26] was used to perform the varus and valgus stress radiographs. After revision surgery, these stress radiographs were repeated in all patients to control extension and flexion gap stability. Medial and lateral stability in extension and flexion was determined by the angle between the tibial base plate and the distal condylar line of the femoral component [26].

Computed tomography according to a standardized protocol [3] was performed in all patients’ prior revision surgery only. Femoral component rotation was measured at the epicondylar level and determined by the posterior condylar angle [3]. The posterior condylar angle was measured as the angle between the posterior condylar and surgical epicondylar line. The posterior condylar line was determined by the posterior tangential line of the femoral component. The surgical epicondylar line was determined by the tip of the lateral epicondyle and the sulcus of the medial epicondyle. In this study, the medial sulcus could be identified clearly in all patients. The posterior condylar angle was classified in three different types (mild ≤3°, moderate 4–6° and severe >6°) of internal malrotation (Table 1). Tibial component rotation was measured at the proximal tibial component and the tibial tubercle level. Tibial component rotation was determined by the angle between the anteroposterior tibial component axis and the tibial tubercle axis [3]. The anteroposterior tibial component axis was determined by the geometric center of the tibial component and the perpendicular to the posterior tangential line of the tibial component. The tibial tubercle axis was determined by the geometric center of the tibial component and the tip of the tibial tubercle. A value of 18° (±3°) of internal rotation was considered to be normal [3].

Long leg radiographs, tangential views, stress radiographs and CT scans were taken and measured by two independent experienced radiographers twice on different days. All measurements were made on a digitally picture archiving system (PACSview, Version 2.51). In all patients, the intraobserver variability was <1° for long leg radiographs, tangential views and stress radiographs. The intraobserver variability was less than 0.5° for CT scans.

According to the records, 4 out of the six knees with a painful limited range of motion had unsuccessful manipulation under anesthesia. In 3 out of the six patients without patellar replacement, an unsuccessful isolated patellar replacement surgery had been performed. Eleven of the 14 (79%) procedures were performed by a flexion gap balanced technique, and 3 by a measured resection technique. Five of the 14 patients had a valgus deformity before the primary TKA. One of the 14 patients had a lateral retinaculum release before the primary TKA. The implants used for the primary TKA was a cruciate-retaining in 8 and a posterior-stabilized prosthesis in six patients. A mobile-bearing system was used in 9, and a fixed-bearing system in five patients. The patella was replaced in seven patients, and one patient had already a patellectomy before the primary TKA.

Surgical revision procedure was performed by a medial parapatellar arthrotomy. The preoperative evaluated flexion and extension stability was assessed by an intraoperative clinical varus–valgus stress test in 20 and 90° or maximal flexion with verifying of the lateral lift-off distance between the femoral and tibial component. Patellar tracking was evaluated with the “no thumb technique,” and the preoperative maltracking could be verified in all cases. The same condylar-type revision implant was used in all patients (legacy condylar constraint knee system, LCCK, Zimmer, Warsaw, USA). The implanted revision system was stem augmented in all patients. To establish a new tibia platform in neutral alignment, rotation and slope, no corrections were necessary. The correct positioning of the new femoral component was established by bony landmarks and soft tissues. First, the medial and lateral epicondyles were identified by dissecting the surrounding scars and preparing the femoral insertion of the collateral ligaments. The epicondylar axis was marked with two pins (Fig. 1a), and rotation correction of the distal femur cuts was performed by removing bone from the lateral ventral to medial posterior parts of the distal femur (Fig. 1b, c). The corrected rotation was controlled by the epicondylar axis (Fig. 1d). For fixation of the rotation correction, a 5- or 10-mm spacer block was used on the lateral posterior condyle of the trial femoral component. The rotational position of the trial femoral component was controlled again by the epicondylar axis (Fig. 2). The clinical varus–valgus stress test was then repeated with the implanted trial components again. The former asymmetry of the flexion gap and condylar lift-off could be abolished in all patients. The goal of the revision surgery was to balance the knee in flexion and extension and use a posterior-stabilized design when ever possible. The evaluation of the patellar tracking with the “no thumb technique” showed normal tracking in all patients after the correction.

Fig. 1
figure 1

a Right knee after the removed femoral component. The internal malrotation of the femoral component is shown by the epicondylar axis not parallel to the posterior condylar line. (b, c) Rotation correction of the distal femur cuts by removing bone from the lateral ventral (b) and medial posterior (c) parts of the distal femur (d) corrected femoral rotation shown by the epicondylar axis parallel to the posterior condylar line

Fig. 2
figure 2

The new rotational position of the trial femoral component controlled by the epicondylar axis

All 14 patients were reviewed at 1, 3, 6 and 12 months after surgery and there after once a year. They were evaluated using the Knee Society Scores (KSS) [12] and the Hospital for Special Surgery (HSS) knee score [13] at the time of initial presentation and at the final follow-up (mean 57 months, SD 12, 46–89).

Statistical analysis

For statistical analysis, a paired t test at the P < 0.05 level to compare prerevision with postrevision scores was performed. A paired t test at the P < 0.05 level to compare prerevision with postrevision femorotibial instability in 20 and 90° flexion determined by fluoroscopically assisted varus–valgus stress radiographs was also performed (SPSS Statistics, Chicago, IL, USA).

Results

At the time of revision, patients suffered either from instability in flexion with good ROM (eight patients with flexion ≥90°, type A) and pain on the lateral side of the distal femur and proximal tibia or from stiffness with pain on the medial side of the proximal tibial and poor ROM (six patients with flexion <90°, type B) (Table 2). In the fluoroscopically assisted varus–valgus stress radiographs, all 14 patients were stable in 20° flexion (Table 3). The 8 patients with the good ROM (flexion ≥90°) had a lateral condylar lift-off in 90° flexion (P < 0.0001, Table 3). All these 8 patients showed giveaway during walking. All patients had difficulties standing up from a seated position and descending stairs. Three patients had moderate pain. Eleven patients had severe pain, and all patients had anterior knee pain at the time of revision. One patient showed no patellar maltracking. Six patients showed a patellar tilt, and six patients showed patellar subluxation (Table 1). One patient had a patellectomy before the primary TKA. None of the 14 patients had a complete patellar dislocation.

Table 2 Functional outcomes after exchange arthroplasty in 14 patients
Table 3 Instability femorotibial in extension and flexion in 14 patients as determined by fluoroscopically assisted stress radiographs

Revision surgery was performed in 14 patients with internal malrotation ≥4° in the CT scans (Table 1). The median internal rotation of the femoral component was 7.1° (4.1–10.0°, Table 1).

A posterior-stabilized insert was used in all 14 patients. A really condylar-constrained insert was not required. Replacement of the patella was performed in all patients but one who had a patellectomy before.

After the revision surgery, no instability in flexion or stiffness has been seen. The mean range of motion was improved (ns type A, P = 0.0027 type B) in both groups (Table 2).

After the revision, no patient showed a lateral condylar lift-off in 90° flexion in the fluoroscopically assisted varus–valgus stress radiographs (ns type A, B, Table 3). Ten patients had no pain, four patients had moderate pain, and no patient showed anterior knee pain or patellar maltracking after the revision. The mean KSS prosthesis/function increased (P < 0.0001/P = 0.001) from 52 (SD 13, 26–69)/65 (SD 19, 30–90) points to 85 (SD 8, 66–94)/84 (SD 12, 65–100) points with revision surgery. The mean HSS increased (P < 0.0001) from 63 (SD 7, 51–74) to 83 (SD 7, 68–91) points. Based on the results of the HSS, six knees were rated excellent, five knees were rated good, and 1 knee was rated fair. No patients had poor results. No complications during and after the revision surgery of the 14 patients were seen.

Discussion

The most important finding of the present study was that patient with malrotated femoral component benefit from the exchange revision arthroplasty.

Internal malrotation of the femoral component has shown to create an asymmetric, unbalanced flexion gap [10, 27, 28], instability in flexion [1], correlation of femoral component malrotation with lateral condylar lift-off [14], stiffness and pain on the medial side of the proximal tibial bone [4, 17] and anterior knee pain [2]. The clinical presentation and significance as well as the amount of internal malrotation causing these different types of symptoms remain still unclear. In this study of patients with isolated internal malrotation of the femoral component, we tried to answer the following questions: type of symptoms at the time of revision, the amount of malrotation leading to revision surgery, which type of constrained is necessary for the revision and do the clinical outcomes improve after revision surgery.

In this study, two distinct types of clinical and radiographic presentations in patients with femoral internal component malrotation could be identified. Type A included good range of motion (≥90°) and lateral flexion gap instability in eight patients (57%). The typical clinical presentation was pain and the feeling of instability with possible painful giveaway during climbing stairs and rising up from a chair. The focus of pain was in the iliotibial band, the lateral capsular-ligament complex as well as in the anterior part of the knee. This might be explained by the insufficient effort of the lateral soft tissues and the anterior extensor mechanism to compensate the asymmetric flexion gap and lateral flexion gap instability. The lateral flexion gap instability and good range of motion (≥90° flexion) had been already described in a study with 18 knees with increased internal femoral component rotation and fewer favorable clinical outcomes [26]. Type B included limited range of motion (<90°), medial catch and progression to secondary arthrofibrosis and stiff knee in six patients (43%). The typical clinical presentation was pain at the medial joint aspect with irradiation to the anterior part of the knee joint. The focus of pain was in the medial capsular-ligament complex and the proximal part of the medial tibia. This might be explained by the general tighter implantation of the insert compared to type A, which causes nonphysiological asymmetric stress in the medial capsular-ligament structures and the proximal tibial bone. In contrast to type A, the lateral flexion gap instability remains clinical not relevant in type B due to the limited ROM. The correlation between internal femoral component malrotation, limited ROM, stiffness and pain at the medial aspect of the knee had been reported already in recent studies [4, 16, 17]. All 14 patients showed more or less anterior knee pain. Six patients with mild and moderate malrotation showed tilting only. However, 6 patients with severe malrotation showed patellar subluxation. None of the patients had an episode of patellar dislocation. This contrasts with previous studies with combined internal malrotation of tibial and femoral components where patellar dislocation had occurred [3, 11].

In the current series, the median internal rotational malalignment of the femoral component was 7.1° (4.1–10.0°) (Table 1). Revision surgery was performed in patients with malalignment of ≥4°. Two patients with mild isolated malrotation (≤3°) could be treated conservatively. However, most of the patients had an internal malrotation >6°. Due to our own experiences and results from the literature [4, 25, 26], we suggest to classify the malrotation of the femoral component in three degrees of severity: mild ≤3, moderate 4–6° and severe >6°. This classification might be confirmed in a cadaver study where 3 and 6° internal rotational alignment of the femoral component has shown different degrees of flexion instability [25]. In another clinical study, patients suffered from painful flexion instability after TKA [26]. The internal femoral malrotation was by a mean of 5.5° compared to asymptomatic patients with normal femoral rotation in this series [26]. In patients who had developed stiffness after TKA, the femoral components were internally rotated by a mean of 4.7° compared to normal patients after TKA [4]. However, no correlation between the amount of femoral malrotation and the type of clinical presentation (instability versus stiffness) could be found in this study.

In the current study, all patients received a revision system that was posterior-stabilized only and no condylar-constrained or hinged implants were necessary. After the correction of the femoral malrotation and balancing the flexion and extension gaps, a posterior-stabilized insert was sufficient enough to stabilize the knee in flexion and extension. This could be verified intra- and postoperatively in all of these patients. In one study of 22 cases with exchange arthroplasty for component malrotation, the revision components used were a posterior-stabilized design in two (9%) cases of isolated femoral revision and a more constrained design in 20 (91%) cases with femoral and tibial malrotation and revision of both components [11]. In this series, seven patients showed clinical relevant instability before revision surgery. In another study of 24 cases with exchange arthroplasty for component malrotation, the revision polyethylene inserts were posterior-stabilized in 22 (91%) cases and varus/valgus constrained in 2 (8%) cases [16].

In the present series, we observed an increase of the mean KSS and HSS scores in all patients. The revision surgery resulted in an improvement of the function with an increase from 65 to 84 points in the KSS function score (P = 0.001). The ROM increased, particularly for patients with stiffness, where the mean increase from 65 to 105° flexion (P = 0.0027) (Table 2). A clinical study reported improvements in ROM and KSS scores after early revision exchange arthroplasty for femoral and/or tibial component malrotation [11]. In this study, the KSS function score increased slightly from 38 to 49 in the average (P < 0.01) [11]. A recent case-control study reviewed 24 patients who had TKA revision due to combined internal malrotation of the tibial and femoral component [16]. Preoperative KSS improved from 33 to 80 points in the maltreated group at last follow-up [16].

A limitation of the present study is the small number of patients. Isolated internal malrotation of the femoral component is rare because additional implantation failures (malalignment, ligament instability and mismatch extension to flexion gaps) are commonly seen in these patients [6, 10, 29]. This was confirmed by our own data, where out of 59 patients with verified malrotation of the components, 16 patients (27%) showed isolated internal femoral component malrotation only. The study group was inhomogeneous related to the revised type of implants, bearings, constrain, patellar replacements and surgical technique. Therefore, no correlation could be identified with the different types of these factors except of the surgical technique. Interestingly, in this study, 79% of all patients were operated by a flexion gap balanced technique. However, a conclusion on the risk of a femoral malrotation by the surgical technique [10, 19] is difficult due to the small number of patients. The wide range of rotational alignment of the femoral component with the flexion gap balanced technique has been confirmed in a computer navigation study [18]. Further studies with larger patients groups might be helpful to identify further risk factors for femoral malrotation. CT scans after the revision surgery to verify the correction of the rotational malalignment of the femoral component were not arranged. From the ethical point of view, it was difficult to perform CT scans in these patients with significantly improved results. However, fluoroscopically assisted stress radiographs showed no lateral lift-off in 90° of flexion after revision surgery. This might be accepted as a clinical confirmation for the successful correction of the femoral malrotation. The possible revision of the femoral component only was not performed in this study. As none of the primary implantations had been performed in our institution using our standard primary implant, our approach was to revise both components using our own standard revision system. The general replacement of the patella was not necessary in these cases, but as we routinely replace the patella in our institution, all patients received a patellar replacement but one, who had a patellectomy before the primary TKA.

Patients with an early painful total knee arthroplasty should be evaluated for malrotation. Infection should be excluded. CT scans and fluoroscopically assisted varus–valgus stress radiographs might be helpful for diagnosis. When component malrotation is demonstrated, revision surgery should be offered to the patient.

Conclusions

The current study supports the opinion that an internal malrotation of the femoral component leads to either symptoms of instability in flexion with good ROM or stiffness with poor ROM. This study showed that early correction of isolated internal malrotation of the femoral component ≥4° might lead to better clinical and functional outcomes in these patients. The results for early revision of painful TKA with internal malrotated femoral component were encouraging, but more studies and results may be necessary for further evaluation of this procedure.