Total Knee Arthroplasty in Coronal Deformities > 15°: Comparison of Short-term Outcomes between Primary and Semi-constrained Implants

Abstract

Objective To compare the clinical and radiological patient outcomes with varus-valgus knee deformities undergoing knee replacement with posterior stabilized (PS) prostheses versus semi-constrained condylar knee (CCK) implants.

Methods Retrospective study of patients with mechanical alignment (MA) > 15°, undergoing PS or CCK. All the procedures were done in the same center between 2014-2018. The decision was determined by clinical, radiological, and intraoperative parameters. Patients with incomplete data and follow-ups of less than one year were excluded. Patient demographic data, pre- and postoperative deformity, range of motion (ROM), complications, and functional outcomes were evaluated from the database.

Results 39 patients met the selection criteria. PS group: 27 patients, mean age of 69 years [49-82]; 59.3% varus and 40.7% valgus. CCK group: 12 patients, mean age of 69.3 years [41-89]; 33.3% varus and 66.7% valgus. The groups had no significant differences regarding demographic data or MA between the groups (p = 0.07). Average follow-up: PS = 49,1 months; CCK = 22 months. The KOOS score was 74.1 for PS and 85.2 for CCK (p > 0,05). WOMAC score was significantly better for the CCK group. The average postoperative ROM was PS = active: 1,9°-101°; passive: 1,6°-108,4° /CCK = active: 2,5-110°, passive: 1,9-117°. Significant differences in active (p = 0.03) and passive (p = 0.04) flexion were observed. The MA correction was PS = 14,9 [3°-31°] / CCK = 19° [13°-28°] (p = 0.09). No infectious or thromboembolic postoperative complications were reported.

Conclusion PS and CCK implants are valid options for patients with coronal deformities >15°. At almost two years of follow-up, the WOMAC Score and flexion significantly improved outcomes with the CCK implant.

Level of evidence IV.

Keywords

knee - knee replacement - severe deformity - semi-constrained - primary replacement - Primary replacement

Introduction

Knee osteoarthritis is a common and disabling pathology, with total knee prosthesis (TKP) being an effective solution for more advanced cases.[1] [2] In our practice, we are increasingly confronted with patients with a significant alteration of the coronal axis and greater joint involvement. Waiting for the resolution of their pathology and the progressive degenerative changes depending on the activity or underlying condition can alter the normal physiological axis and generate severe angular deformities.

One of the keys to the success and long-term survival of the prosthetic implant is to achieve adequate alignment and joint stability; however, in the case of more severe deformities, this objective can become a complex scenario.[3] [4] Joint imbalances are a challenge in TKP surgery given their association with ligamentous instability, joint stiffness, and/or bone defects.[5] If the correction obtained and the soft tissue balance allow symmetrical tension of the implant in both flexion and extension, a standard primary prosthesis can be used.[6] But if we are faced with residual laxity associated with suboptimal balance, we must use an implant with a greater degree of varus-valgus constriction.[7] [8] [9]

The current trend in complex situations is towards preferring more constrained implants that ensure stability;[10] however, these have a high economic cost,[11] and the evidence is limited regarding their functional results and long-term survival.[12] In addition, there are certain theoretical disadvantages associated with the use of constrained prostheses, such as the potential mechanical loosening secondary to the transfer of loads towards the bone interface that leads to early failure and/or periprosthetic fracture.[13] [14] Likewise, the wear of the polyethylene insert is another possible drawback.[15]

Consequently, the literature has questioned what type of implant is required to predictably and successfully correct the deformity in cases with deviations greater than 10° or 20°,[5] [6] [7] [9] [16] [17] [18] prompting us to review our approach in this regard. Therefore, the objective of the present study is to describe the clinical, functional, and imaging outcomes in a population of patients with varus or valgus alteration of at least 15° in the coronal plane, comparing the use of posterior-stabilized versus semi-constrained prostheses.

Methods

A series of patients with knee osteoarthritis and greater angular deformity in the varus or valgus who underwent total knee prostheses in our hospital between January 2014 and December 2018 were retrospectively analyzed. Those patients with a mechanical axis greater than 15° of varus or valgus in which a primary posterior stabilized (PS) or semi-constrained condylar knee (CCK) arthroplasty was performed. The following exclusion criteria were considered: extra-articular deformities, a follow-up of less than one year, and an incomplete record of clinical and/or radiological data. Patients were scheduled by telephone for clinical and radiological monitoring by an evaluator independent of the surgical team. Follow-up was defined as the time between the index surgery and the evaluation. Authorization was obtained from the establishment's ethics committee.

Determination of the implant to be used

The decision to use a PS or CCK prosthesis was determined by radiological and clinical parameters and intraoperative factors. Using preoperative teleradiography, the level of cut required to bring the mechanical axis of the knee to neutral was planned for each case. In those cases, in which there was a bone defect greater than the cut estimate in the distal femur or proximal tibia, the use of an CCK prosthesis with augmentation blocks was considered preoperatively. Among the clinical factors, the patient's age, joint stiffness, and stability of the collateral ligaments were evaluated. Given collateral ligament insufficiency, the decision for CCK was also made preoperatively. In younger patients, we always tried to use the lowest level of constriction, however in all those cases in which an adequate balance of flexion and extension was not achieved, despite the planned bone cuts and the careful release of soft tissues, we resorted to an intraoperative CCK implant. To do this, the femoral and tibial cuts were made again according to the specific cutting guides, balancing the soft tissues and evaluating the need to use augmentation blocks if necessary. We used a spacer block to assess space in extension and flexion, manually applying varus and valgus stress in extension, midflexion, and 90° flexion. An extramedullary rod was used to evaluate the intraoperative axis. In all cases of deformity greater than 15°, it was requested to have a set of revision prostheses in the operating room as a backup.

Rehabilitation

Rehabilitation began in all cases the day after surgery with kinesiological support. Passive and active mobilization were initiated, as well as weight-bearing walking with 2 crutches. Hospital discharge was decided once adequate analgesic management and the ability to walk were achieved. All patients received deep vein thrombosis prophylaxis.

Radiological evaluation

Full-leg standing digital radiographs was performed, and the mechanical axis of the knee was determined pre- and postoperatively for all patients in the study. The mechanical axis of the knee is defined by the angle that connects the mechanical axis of the femur and tibia.[19] The axis was expressed as a deviation of 180°, with varus being defined as an angle of -3° or less and valgus as an angle of +3° or more. For postoperative measurement purposes, an angle between -3° and +3° was defined as a neutral axis. The last postoperative radiograph also confirmed the presence of loosening and other visible complications, such as subsidence or periprosthetic fracture.

Clinical evaluation

The Knee Injury and Osteoarthritis Outcome Score (KOOS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) functional evaluation questionnaires in Spanish were administered to all patients at the end of follow-up.[20] [21] The range of final joint mobility of the active and passive knees of the operated knee was evaluated through physical examination and the use of a goniometer by an evaluator independent of the surgical team. Through the clinical record, the hospital stays of each patient and the early or late complications that may have occurred associated with the surgery were recorded, such as thromboembolism, hemorrhage, infection, dislocation, periprosthetic fracture, and/or surgical reintervention.

Analysis of data

A comparative statistical analysis was performed using the StatPlus for Mac® program. A normal distribution analysis (Shapiro-Wilk) was performed on the demographic variables and results. The data of the studied population were compared using a T-test for age variables and axes of deformity, and a Chi-square for gender variables. In the analysis of results, non-parametric statistics (Mann-Whitney U) were used for comparative analysis of WOMAC, KOOS and the range of joint mobility. The Spearman correlation was used for the analysis of range of mobility versus insert, and Kruskal-Wallis's test was used to evaluate mobility according to the prosthesis model. The analysis of axes and their degree of correction was performed with a t-test and chi-square was used for the analysis of the results of grouped axes. A p value < 0.05 was considered significant.

Results

There were 27 patients undergoing primary stabilized posterior arthroplasty and 12 patients in whom a semi-constrained implant was used. One patient with a CCK implant was excluded from pre-analysis due to a lack of follow-up. Demographic data for both groups is summarized in [Table 1]. The hospital stay was shorter in the CCK group (p = 0.19).

Table 1

Demographics	PS N = 27		CCK N = 12	p value
Average Age (years)	69 (range 49-82)		69,3 (range 41-89)	0,82
Gender
Female	19 (70.4%)		6 (50%)
Male	8 (29.6%)		6 (50%)	0,22
Preoperative axes
Varus	16 (59.3%)		8 (66.7%)	0,66
Valgus	1 (40.7%)		4 (33.3%)
Prosthesis	Scorpio®	10	Legion CCK® 12
	Scorpio® NRG	5
	NexGen®	3
	Genesis II®	9
Follow-up (months)	49,1		22	0,41
Hospital Stay	3,8 days		2,3 days	0,019

Clinical results

The mean KOOS score at the end of follow-up was 74.1 for the PS group and 85.2 for CCK, without significant differences between both groups. When analyzing the KOOS subscales, it was observed that in the pain item, the score was 86.4 points for the PS group and 94.9 points for the CCK group (p = 0.02), and in the daily life activities it was 77.1 for the PS group and 91.8 for CCK (p = 0.003). There were no differences in the other subscales ([Table 2]). The analysis of the WOMAC scale found significant differences in favor of the CCK group in all subcategories ([Table 3]).

Table 2

KOOS	PS	CCK	p value
SYMPTOMS	86.1	94.7	0,05
PAIN	86.4	94.9	0,02*
ADL	77.1	91.8	0,003*
SPORTS	42.6	57.5	0,25
QUALITY OF LIFE	78.4	87.0	0,09

Table 3

WOMAC	PS	CCK	Valor p
PAIN	9.8	5.7	*0,04
RIGIDITY	6.4	1	*0,03
FUNCTIONAL CAPACITY	24.9	8.6	*0,00

The passive range of motion (ROM) of the joint was 0°-1.6°-108.4° for the PS group and 0-1.9°-117° for the CCK group. The active ROM of the joint was 0°-1.9°-101° in the PS group and 0°-2.5°-110° in the CCK group, active and passive flexion presenting a statistically significant difference between both groups in favor of the CCK prostheses. There was no difference in active or passive extension ([Table 4]).

Table 4

ROM	PS	CCK	p value
active flexion	101.0	110.0	0,03*
active extension	1.9	2.5	0,93
passive flexion	108.4	117.0	0,04*
passive extension	1.6	1.9	0,86

The range of mobility was analyzed according to the prosthesis model used for the PS group without finding a statistical difference for this variable ([Chart 1]). The range of active flexion and extension according to insert size was also evaluated in both groups without finding a statistical correlation (r = 0.12 flexion/r =0.22 extension).

Chart 1 Active flexion range according to posterior-stabilized (PS) prosthesis model. No statistically significant differences were found. (Kruskal Wallis, p = 0,48).

Radiological results

The preoperative radiological evaluation showed that in the PS group, 16 patients with genu varum (59.3%) had an average mechanical axis of 18° (range 15° to 28°) and 11 patients with genu valgum (29.6%) had an average axis of 18.3° (range 15° to 26°). In the CCK group, 8 patients with genu varum (66.7%) had an average mechanical axis of 22° (range 15° to 31°), and 4 patients with genu valgum had an average axis of 17.3° (range 15° to 31°). No significant differences were found between the groups (p = 0.68). In the postoperative radiological evaluation, the average mechanical axis in the PS group was 5° of varus (range -13° to 5°), and in the CCK group, it was 0.6° of varus (range -7° to +6°). The average correction was 14.9° (range 3° to 31°) for the PS group and 19° (13°-28°) for the CCK group (p = 0.08). When categorizing the postoperative axes as neutral (-3° to 3°), we found that 9 (33%) patients in the PS group and 7 (58%) in the CCK group fell within this range. This difference did not reach statistical significance (Chi[2] = 0,07). ([Table 5])

Table 5

AXIS	PS (N = 27)	CCK (N = 12)	valor p
Pre-operative
Varus	18° (15°-28°)	22° (15°-31°)	T-test
worth	18, 3° (15°-26°)	17, 3° (15°-31°)	0,68
Postoperative
Average	Varus 5°	Varus 0,6
Range	(varus13° a valgus5°)	(varus7° a valgus6°)
Varus	17	4
valgus	1	1
neutral	9	7	Chi2
%neutral	33%	58%	0,07
Correction	14, 9°	19°	0,09

Implants used

In the 12 patients in the CCK group, the Smith & Nephew Legion CCK® implant was used with femoral and tibial stems, using hybrid fixation (cemented articular component and uncemented stem). In 7 patients, the determination to use a CCK implant was made preoperatively: 6 due to a bone deficit that required the use of a tibial augmentation block and 1 due to instability of the medial complex. Additionally, femoral augmentation blocks were used in 4 patients.

Complications

No thromboembolic, hemorrhagic, or infectious complications were reported in the evaluated patients. No periprosthetic fractures were reported either. One patient in the EP group required mobilization under anesthesia three months after the index surgery, and another patient in the same group experienced a traumatic dislocation. This was due to unauthorized early ambulation with femoral nerve block, which compromised the medial ligament and was satisfactorily managed with conservative treatment. No reoperations or revision surgeries were reported in either group until the end of the follow-up. No loosening was found in the radiographic study.

Discussion

The main finding of this study is the fact that semi-constrained prostheses show comparable results to prostheses with posterior stabilization, even showing a trend towards better functional scores.

The literature is not homogeneous in defining a threshold of degrees of coronal deviation for complex prostheses and the use of greater constraint.[10] That is why we have based our approach on authors like Long and Scuderi,[5] who, in their chapter on varus and valgus deformities for complex arthroplasty, mention that deviations greater than 15 degrees will require greater challenges in planning. In the study, we did not find differences in the age group of patients who received each of the implants; however, we believe that the use of PS prostheses is our first option in younger patients, where the preservation of bone stock is an important consideration for a future revision. On the other hand, in older patients, the option of a CCK implant that guarantees stability seems to offer a safe outcome in terms of mobility and function.

Preoperative planning is always essential to define whether it is possible to use a standard primary implant. Koninckx et al.[22] demonstrated that it is possible to manage severe deformities without the need to use a constrained implant, through minimal bone resection and balanced soft tissue release. In a genu valgus, a possible hypoplasia of the lateral femoral condyle must be considered, so the planning of the cut must be carried out in the full-leg standing radiographs and the difference between the mechanical axis of the femur and the anatomical axis must be measured, to define the graduation of the distal cutting guide to be used. It is commonly thought that this value is between 5° and 7°, but its verification allows us greater precision in the resection and preoperatively define the cases that may require an augmentation block.[23] [24] Tibial resection in the genu valgus must consider an eventual extra-articular deformity at the diaphyseal level, which will require centering the tibial guide slightly medial to the center of the plateau.[25] In varus deformity, it should be considered that the proximal center of the cutting guide generally faces the lateral spine to coincide with the anatomical tibial axis.[26] At this point, we believe the routine use of an intramedullary cutting guide is beneficial; following these technical considerations, more severe deformities can be successfully managed with an PS implant. The planning also allowed us to identify which patients had a bone deficit that would require augmentation blocks. In the six cases in the CCK group where this block was used on the tibial plateau, the implant to be used was determined preoperatively.

There are cases where a higher degree of constraint is required due to pre-existing ligament insufficiency. This is particularly important in valgus deformities, where there is greater residual laxity of the medial collateral ligament, which can excessively complicate achieving optimal balance during surgery.[7] In turn, this type of deformity can be associated with hyperextension, which is why the use of an implant with greater constriction is especially useful in these cases.[3] In our series, of the 6 patients with genu valgus who required a CCK implant, 1 patient had a sequelae of poliomyelitis with genu valgus and severe insufficiency of the medial collateral ligament, in which case the determination of the implant to be used was defined preoperatively.

Knees with severe deformities may also be associated with significant stiffness that will require more aggressive release and, therefore, greater care to achieve symmetry. In general, in knees with genu varus, contracture of the medial structures is associated with a flexion contracture. Resection of the osteophytes and release of the pes anserina tendons superficial to the medial collateral ligament will be required to obtain better symmetry. The use of techniques such as “pie-crusting” on the medial ligament can also be helpful.[27] Stiffness and deformity can also be associated with post-traumatic sequelae, so the presence of scars can guide us regarding the insufficiency of certain structures that force us to use a CCK implant.[28]

As we have mentioned, when comparing the functional outcomes between both groups, there were significant differences in favor of the CCK group for the WOMAC scales and the pain and ADL items of the KOOS scale. We cannot determine if the shorter hospital stay for the CCK group was due to less pain in the immediate postoperative period (less soft tissue intervention) or changes in multimodal analgesia.

Regarding the range of motion evaluated postoperatively, we did not observe differences in extension, but we did observe significantly greater flexion ranges in the CCK group versus the PS group. It has been described that preoperative range of motion is a determinant factor of postoperative mobility.[29] However, a limitation of our analysis is the lack of preoperative range of motion records. On the other hand, our CCK series presented results similar to those of other studies that have reported average mobility ranges of 113° and 117° for constrained prostheses.[28] [30] They suggest that they achieved good ranges of motion regardless of preoperative stiffness, so proper insert stability and rehabilitation are key. We believe another point to consider regarding joint mobility is that greater release may leave a larger flexion and extension gap, which would require the use of a thicker polyethylene insert if using a PS implant. Lanting et al.[31] described that if the polyethylene increased by 1 mm in thickness, it would have a significant impact on the possibility of achieving full extension but not on flexion. However, in our study, we did not find a relationship between the size of the polyethylene insert and its range of mobility.

In our series, we did not find cases of revision for either of the 2 types of implants. There are studies that have reported a revision rate twice as high (due to aseptic loosening, infection, or periprosthetic fracture) for constrained vs. non-constrained prostheses.[12] In this regard, we must consider that the average follow-up in our CCK group was only 22.8 months. Furthermore, in our series, the use of femoral and tibial stems was necessary in all cases in the CCK group. While we know that these increase costs and can make future revisions more difficult, there is some controversy regarding the use of femoral stems. It has been described that the use of an implant without a stem in the femur would not increase the risk of loosening,[8] [32] however, this technique requires adequate bone stock and quality, a requirement not present in all our patients.

The main limitations of our study are the short follow-up, low N, and not having preoperative range of motion. We could also consider having different PS prosthesis models as a limitation. The low N does not allow a subanalysis to be carried out, but at least in range of mobility, no differences were found between one model and another. In any case, we highlight the importance of documenting the results of implants with different levels of constriction in this type of deformity.

Conclusion

In patients with knee osteoarthritis and coronal deformities > 15°, proper patient selection and meticulous preoperative and intraoperative planning allow for management with both PS and CCK prostheses as valid options. The clinical, radiological, and functional outcomes are similar, but there are significantly greater flexion and WOMAC scores in the CCK prosthesis group after nearly 2 years of follow-up.

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Publication History

Received: 05 October 2022

Accepted: 01 July 2024

Article published online:
25 September 2024