The use of a modern robotic system for the treatment of severe knee deformities

Abstract

BACKGROUND:

Robotic-assisted total knee arthroplasty (TKA) have shown promising results in recent years with improved clinical outcomes using standard primary implants.

OBJECTIVE:

The purpose of this study was to assess the experience of a single center in correcting severe coronal deformities with the use of a robotic-assisted TKA system and an increased constrained implant.

METHODS:

Between July 2020 and December 2022, 30 knees in 28 patients with a major deformity and an associated ligament laxity requiring an increased constrained implant treated using an imageless robotic-assisted TKA were prospectively enrolled. Patients included in the study showed a minimum 15 degrees varus or 10 degrees valgus deviation.

RESULTS:

20 cases were varus knees and 10 cases were valgus knees. Postoperative neutral alignment was defined as 0^∘ $\pm$ 2.5^∘. A CCK implant was used in 20 cases while a Constrained Posterior Stabilized implant was used in 10 cases. A neutral alignment was achieved in all patients. At a minimum 6 months follow up (f-u 6–30 months) clinical outcomes including ROM, KSS, HSS, OKS and WOMAC showed significant improvement and no major complications were registered.

CONCLUSIONS:

The robotic system showed the achievement of a mechanical alignment with reliable radiographic outcomes and clinical results in the treatment of major deformities of the lower limb with the use of higher constrained implants at short term follow up. Further follow up and studies are necessary to confirm and verify these promising outcomes.

Keywords

Robotics knee major deformities varus valgus constaint computer-aided surgical planning orthopedic surgery

1. Introduction

Robotic-assisted total knee arthroplasty (TKA) has shown promising results in recent years. The majority of the studies recently published have shown improved outcomes with the use of standard primary implants [1, 2]. Current research has shown the possibility to obtain a functional or individualized alignment on all 3 planes with the robotic technology.

Ensuring correct coronal alignment plays a crucial role in enhancing patient function and promoting the long-term durability of knee implants during the progression of constraint levels in total knee arthroplasty (TKA) [3, 4]. The primary objective in addressing significant deformities is often to establish a neutral classical mechanical axis alignment. However, achieving this alignment can pose challenges, particularly when dealing with severe varus or valgus knees [5]. Substantial preoperative coronal deformities can lead to an increased risk of implant failure, and rectifying the deformity can mitigate this risk of failure [6, 7, 8].

Although robotic-assisted TKA has also shown the potential to accurately reproduce neutral alignment, it is still unclear if this correction is attainable in patients who have severe varus or valgus deformities and therefore be used with more constrained implants [5, 9].

The purpose of this study was to assess the experience of a single center in correcting severe coronal deformities with the use of a new robotic-assisted TKA system and a more constrained implant device.

Specifically, the correction of varying degrees of varus and valgus deformity and the clinical outcomes in patients who underwent robotic arm-assisted TKA were analyzed and reported.

2. Materials and methods

Between July 2020 and June 2022, 30 knees in 28 patients with a major deformity and an associated ligament laxity, requiring an increased constrained implant, were treated using a robotic-assisted TKA with the ROSA robotic system in its image-less version and a constrained posterior stabilized (Persona CPS) or a condylar constrained implant (LCCK, Zimmer Biomet Warsaw, Indiana). Patients included in the study showed the following features:

•
Severe valgus deformities ( $>$ 10 degrees), type 2 or 3 according to the Ranawat classification [10, 11], 2-3-4 according to Krackow, or type 3, 4, 5 of the Mullaji and Shetty classification, which might require substantial soft tissue release potentially ending with a residual varus-valgus laxity [12, 13].
•
severe varus deformity ( $>$ 15 degrees fixed intra-articular deformity) type 3–4 according to the Thienpont and Parvizi classification with varus thrust which requires a soft tissue release resulting in a mild medial instability or severe metaphyseal deformity according to the same classification [14, 15].
•
post-traumatic deformities or severe arthritis secondary to complex ligament reconstructions with ligamentous insufficiency and/or intra-operative MCL instability [16].

Patients’ demographics are summarized in Table 1 and deformity was classified as follows:

•
20 cases were $>$ 15 degrees varus knees
•
10 cases were $>$ 10 degrees valgus knees.

All patients were treated with the ROSA robotic system using the surgical technique described by Battailer et al. [2] and Rossi et al. [17], aiming for a neutral alignment $\pm$ 2.5 degrees to achieve the best gap balancing.

Procedures were undertaken by the senior authors, using a mid-parapatellar approach.

The choice of implant was in all cases taken preoperatively using the criteria exposed by Rosso et al. [16] and Mancino, Rai and Alqatub et al. [3, 18, 19] and confirmed intraoperatively after gaps and ligament evaluation showing a discrepancy or a laxity of more than 3 mm and confirming the need for the use of an increased constraint.

The ROSA robotic system allows a ligament evaluation of both medial and lateral compartments at different degrees of flexion (0-30-60-90 and 120^∘) and during different phases of the surgical operation (pre, intra-op, and final evaluation). A discrepancy of more than 3 mm (between 3 and 5 mm) between the medial and lateral compartment at 0 and 30^∘ after the distal femoral and proximal tibial cut or a medial laxity at 60 or 90^∘ of more than 3 mm suggested the use of a CPS implant, while a discrepancy of more than 5 mm in extension or a discrepancy of more than 3 mm between the flexion and extension space suggested the use of CCK implant.

Patients followed a standardized post-operative fast track rehabilitation protocol and were followed at 1-3-12 months postoperatively and then yearly.

The postoperative rehabilitation plan included immediate full weight-bearing with support from one or two crutches for the first 4 weeks. Exercises focused on promoting active flexion and extension. Patients received routine venous thromboembolism (VTE) prophylaxis with low-molecular-weight heparin for 4 weeks after surgery, along with perioperative prophylactic antibiotics (cefazolin). Postoperative clinical and radiological assessments were scheduled at 3 months, 6 months, 1 year, and annually thereafter. Clinical evaluations were based on various scoring systems, including the Knee Society Scoring System (KSS), the Hospital for Special Surgery (HSS) knee scores, the Western Ontario and McMaster University (WOMAC) score, and the Oxford Knee score, in addition to Range of Motion (ROM) measurements. Patients were also asked to rate their results as excellent, very good, good, fair, or poor. All patients underwent pre- and postoperative weight-bearing x-rays to assess limb alignment, component positioning, and the presence of radiolucent lines, following the Knee Society Roentgenographic Evaluation System. The minimum follow-up was 6 months, mean follow up was 18 months (6–30 months).
2.1 Radiographic evaluation

A total of 20 cases were varus knees and 10 cases were of valgus knees.

A severe deformity was defined as 15^∘ or greater for the varus deformity and 10^∘ or greater for the valgus deformity: type 2 (moderate ) or 3 (severe) according to the Ranawat classification [10, 11]. Postoperative neutral alignment was defined as HKA angle of 0^∘ $\pm$ 2.5^∘. Postoperative coronal alignment measurements were taken at the 3 months follow up long standing x-rays.

2.2 Statistical analysis

Statistical analysis was carried out by an independent statistician. Data were collected with Excel^® Microsoft. Continuous variables were described using arithmetic mean and SD (standard deviation). Categorical variables were described using frequency distributions and percentages. T test and chi-squared test were performed with Medcalc to analyze differences in continuous and categorical variables, respectively. Survival Analysis was conducted using the Kaplan-Meier methodology according to different end points with the associated 95% confidence intervals.

The study was performed in accordance with the ethical standards of the 1964 Declaration of Helsinki and with the HIPAA regulation. The study was approved by the local ethical committee.

3. Results

3.1 Clinical outcomes

No patients were lost at follow-up. 30 implants were included in the study. There were 15 females (1 bilateral 55%) and 13 males (1 bilateral 45%), with an average age of 59.8 $\pm$ 11.3 years and an average Body Mass Index (BMI) of 24.9 $\pm$ 3.7 kg/m². The average follow-up was 18 months (6–30 months), with a minimum follow-up of 6 months. Essential demographics and pre-op data are summarized in Table 1.

Table 1
Baseline characteristics and clinical pre/intra-operative evaluation (BMI $=$ Body Mass Index; ROM $=$ Range of Motion, SD Standard Deviation)

Gender (male%/female%)	13 (45%)/15 (55%)
Average age (years)	59.8 $\pm$ 11.3
Average BMI (Kg/m²)	24.9 $\pm$ 3.7
Average follow-up	18 (6–30 months)
Side (right%/left%)	16 (51.1%)/14 (48.9%)
Diagnosis (%)	• Primary idiopathic knee arthritis $\rightarrow$ 20 (67%) • Rheumatoid Arthritis $\rightarrow$ 1 (3%) • Post-Traumatic $\rightarrow$ 9 (30%)
Alignment (%)	• Valgus (Ranawat type 2) $\rightarrow$ 5 • Valgus (Ranavat type 3) $\rightarrow$ 5 • Total Valgus $\rightarrow$ 10 (33.3%) • Varus $\rightarrow$ 20 (66.7%)
Pre-op HKA alignment (mean and SD)	• Valgus Knees: 19.6^∘ (2.7) • Varus Knees: 13.4^∘ (2.5)
Pre-op ROM (^∘)	100.3^∘ $\pm$ 13.1^∘,
Patella replacement	• Replaced $\rightarrow$ 97% • Not replaced $\rightarrow$ 3%

The diagnosis was primary idiopathic knee arthritis in 20 cases (67%), rheumatoid arthritis in 1 case (3%), post-traumatic or post ligament reconstruction arthritis in the remaining 9 cases (30%). Nine patients underwent previous surgery on the same knee (30%), including ORIF (open reduction and internal fixation) ligaments reconstruction, meniscectomy and high tibial osteotomy.

An LCCK implant was used in 20 cases (15 varus/5 valgus) while a CPS implant was used in 10 cases (5 varus/5 valgus).

The mean preoperative flexion angle was 100.3^∘ $\pm$ 13.1^∘, and 25 knees (83%) showed a loss of extension averaging 7.3^∘ $\pm$ 4^∘. All patients exhibited mild to severe mediolateral instability before the operation, primarily linked to deformities or previous traumatic incidents. In 29 knees (97%), the patella was replaced. All postoperative outcomes were assessed at the latest available follow-up.

Following the surgery, the range of motion (ROM) significantly improved from 100.3^∘ $\pm$ 13.1^∘ to 119.8^∘ $\pm$ 8^∘ ( $p<$ 0.0001). Objective and subjective scores, including KSS, HSS, OKS, and WOMAC, demonstrated significant enhancements from the preoperative status to the last follow-up, as indicated in Table 2. A total of 27 patients rated their results as excellent or very good (91%), while 3 patients rated them as good or fair (9%), and none expressed dissatisfaction with the outcome. Throughout the various follow-up assessments (both clinical evaluation and score assessment), all knees remained stable.

Table 2

Summary of outcomes (ROM $=$ Range of Motion; KSS $=$ Knee Society Scoring System, HSS $=$ Hospital for Special Surgery; WOMAC $=$ Western Ontario and Mc Master University; OKS $=$ Oxford Knee score; N/A $=$ Not applicable)

Outcomes	Pre-operative		Post-operative		$P$ -value
ROM	100.3^∘	$\pm$ 13.1^∘	119.8^∘	$\pm$ 8^∘	$p<$ 0.0001
KSS objective	41.8	$\pm$ 18	85.7	$\pm$ 11	$p<$ 0.0001
KSS functional	35.5	$\pm$ 21.4	88.9	$\pm$ 13.2	$p<$ 0.0001
HSS score	54.4	$\pm$ 12.5	89.7	$\pm$ 3.5	$p<$ 0.0001
OKS	17.2	$\pm$ 6.3	40.2	$\pm$ 12.5	$p<$ 0.001
WOMAC
Pain	19.9	$\pm$ 5.7	3.2	$\pm$ 3.8	$p<$ 0.0001
Stiffness	5.8	$\pm$ 2.4	1.5	$\pm$ 1.4	$p<$ 0.0001
Function	50	$\pm$ 14.1	10.6	$\pm$ 10.5	$p<$ 0.0001
Rated outcomes	N/A		– Excellent $\rightarrow$ 70%		N/A
			– Very Good $\rightarrow$ 21%
			– Good $\rightarrow$ 6%
			– Fair $\rightarrow$ 3%

No major complications or deep infections occurred. Minor issues were observed in 7% of cases, including moderate bleeding in one patient, loss of extension in one case, and one case of superficial wound infection, which was successfully treated with antibiotics. Notably, no patients required revision surgery. When considering revision as an endpoint, the cumulative survivorship, calculated using the Kaplan-Meier method, reached 100% at 30 months.

3.2 Radiographic results

Patients with varus and valgus knees were radiographically analyzed as two different overall cohorts; Varus knees were 20 ( $>$ 15^∘); the mean varus deformity was 19.6^∘ (SD 2.7). A LCCK implant was used in 15 cases while a CPS implant was used in 5 cases.

There were 10 cases of valgus knees. All patients had an initial 10^∘ or greater valgus knee alignment (mean 13.4^∘, SD 2.5). A LCCK implant was used in 5 knees while a CPS implant was used in 5 knees.

During the radiological assessment, conducted in accordance with the Ewald classification, there were no notable progressive radiolucent lines. Specifically, one patient with a CCK implant exhibited two minor ( $<$ 2 mm) and non-progressive radiolucent lines around the femur (classified in zones 3 and 4). Additionally, three patients (two in the CCK group and one in the CPS group) displayed non-significant and non-progressive radiolucent lines beneath the tibial component (classified in zones 1, 3, 6, and 7). Notably, in two of these cases (one in each group), the radiolucent lines were already visible in the immediate post-operative x-ray, likely attributed to imperfect cementation techniques.

Table 3
Average angles calculated according to the Knee Society total knee arthroplasty roentgenographic evaluation and scoring system

	Alfa ( $\alpha$ )	Beta ( $\beta$ )	Gamma ( $\gamma$ )	Delta ( $\delta$ )	HKA
Average angle	91.7^∘	88.9^∘	3.5^∘	88.9^∘	179.5^∘
Standard deviation	2.8	1.2	2.3	2	2.1

The positioning of the implants was assessed using the angles described by Ewald. All implants were determined to be correctly positioned, for a mechanically-aligned knee implant (refer to Table 3), with an average Hip-Knee-Ankle (HKA) angle of 179.5^∘ $\pm$ 2.1^∘. Figure 1 illustrates a preoperative x-ray and the radiographic outcome 24 months after surgery for a patient with a severely varus knee, while Fig. 2 depicts a case of a severely valgus knee. No indications of implant instability were observed in anterior-posterior (ap) and lateral (ll) views, nor in long-standing x-rays.

Figure 1.

Pre-operative and 24 months after surgery x-rays of a bilateral severe varus knee.

Figure 2.

Pre and postop images of a severe valgus knee.

4. Discussion

The main finding of this study is that a robotic system can be helpful for the choosing the level of constraint and for addressing major knee deformities with promising results and survivorship at short term.

This is to our knowledge the first clinical series showing the application of a robotic technology on major deformities in knee arthroplasty.

Previous studies have shown good outcomes with the use of increased constrained implants in the treatment of osteoarthritic knees with major deformities.

Valgus knees Ranawat type 1 or 2 were successfully treated by Indelli et al. [20] with a different and lower level of constraint using a J curved CR implant with a medially congruent liner. This study showed interesting results in this cohort of patients with a mean HKA of 11.6 degrees of valgus. Differently valgus patients in the current study had a minimum 10^∘ deformity with 5 patients classified as type 2 and 5 as type 3.

Rosso et al. [16] demonstrated promising clinical outcomes and survival at mid-term with the use of the CPS implant, an intermediate constrained implant indicated for mild to major deformities and ligament laxities on a cohort of 47 knees distributed in two centers.

Alqatub et al. [19] showed good clinical outcomes at 5 years in the treatment of severe varus knees in 56 patients using a CCK implant. In their study only 7% of patients showed poor results. Similar clinical results have been presented by Mancino et al. [21] on 49 patients and 54 knees at 9 years follow up with a survivorship 93.6%. Both studies aimed for a neutral alignment of the limb in the post-op long standing x-rays. Good long-term outcomes are confirmed by Cholewisky et al. [6] in their cohort of 43 knees allowing the authors to conclude that long-term functional gains after CCK TKA were similar to those reported after standard posterior-stabilized TKA, with no cases of constraint-mechanism failure or osteolysis. Lower survivorship in their study (88.5% at eleven years, 97.7 excluding infections) was justified by particularly severe knee deformities and/or instability and a history of one or more surgical procedures in two third of the cases.

In the current study both CPS and LCCK implants are evaluated as an overall cohort confirm promising outcomes and a 100% survival at short term. There are only few studies evaluating the use of a robotic technology in the treatment of major deformities of the knee.

Marchand et al. [22] describe the surgical technique with a CT-based robotic system (Mako) on a series of 3 difficult cases where a post-op neutral alignment was aimed and achieved. The same author published an article describing the use of the Mako robotic system for the correction of severe deformities [5]. The authors defined a deformity severe if the deviation from neutral was $>$ 7^∘ and considered it successfully treated if gaining a postoperative neutral alignment of 0 $\pm$ 3^∘. Out of 129 severe varus knees, 82 knees were corrected to neutral (mean 2^∘, range 0–3^∘) and roughly 30% of patients were not corrected to neutral but still corrected within a couple of degrees of neutral. There were seven knees with 7^∘ or greater valgus deformity, and all were corrected to neutral (mean 2^∘, range 0–3^∘). Differently from the present study, the authors don’t report about clinical outcomes of these series of patients, used primary implants and analyzed less severe deformities.

Finally, the same group also published results on a larger series of valgus knees using the same robotic system and showing good clinical outcomes and a 100% survival [23].

For all the three above studies the authors describe as complex cases pre-op deformities that are inferior to those described in the current series and a standard primary implant was used to address them.

Cook-Richardson and Desai [24] present a complex case of extra-articular deformity of the knee treated with a Mako Robotic assisted TKA showing a good clinical outcome and a satisfactory post-operative mechanical alignment achieved.

Masilamani et al. [25] describe a robotic technique for correcting severe varus deformity, but don’t report clinical or radiographic outcomes with their method while Rothfusz et al. [26] report on a single case report of correction of a severe varus posttraumatic case

In their editorial, Ross et al. [27] conclude that early evidence for the use of these emerging technologies for deformity correction and revision cases is promising, but their impact on long-term functional outcomes remains to be demonstrated. They suggest further studies to be pursued.

Finally, Matassi et al. [28] showed interesting clinical and radiographic outcomes in 18 patients using an accelerometer-based navigation that helped to accurately achieving neutral mechanical alignment and optimal implant positioning in patients with extra articular deformities.

The above-mentioned studies justify the choice of aiming for a mechanical alignment in the type of deformities treated and the increased constraint chosen. This study has some limitations. This is a prospective single cohort study with no matching group. However, each case was performed using a described and reproducible surgical technique providing consistency between cases and results have been evaluated and compared with the outcomes of previous studies on a similar population. Sample size is small and follow up is short (a minimum 6 months follow up represents a major limitation), but at current time these data represent the largest case series available in the literature. Finally, series refer to an heterogenous group of patients (valgus versus varus, posttraumatic and primary degenerative). Results and survivorship at present time are interesting and promising with the robotic assistance showing to be helpful to achieve a mechanical alignment and in the choice of the constraint level of the implant.

5. Conclusions

This study analyzed a single center experience using a new robotic-assisted device to help correcting severe varus or valgus knee alignment to neutral with an increased constraint total knee arthroplasty system.

The ROSA robotic system showed the achievement of a mechanical alignment with reliable radiographic outcomes and clinical results in the treatment of major deformities of the lower limb with the use of higher constrained implants at short term follow up. Further follow up and studies are necessary to confirm and verify these promising outcomes.

Funding

None to report.

Author contributions

SMPR designed the study and was responsible for the manuscript, LA and LM were responsible for the clinical follow up of the patients, and RS and FB revised the manuscript. All authors read and approved the final manuscript.

Ethics statement

The study was approved by the local ethical committee (IRB approval no. NK5022).

Footnotes

Acknowledgments

None to report.

Conflict of interest

FB declares a teaching contract with the manufacturer (Zimmer Biomet). FB also received grants from Limacorporate and royalties from Zimmer Biomet and Limacorporate. The other authors have no disclosures.

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The use of a modern robotic system for the treatment of severe knee deformities

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Materials and methods

2.2 Statistical analysis

3. Results

3.1 Clinical outcomes

Table 1 Baseline characteristics and clinical pre/intra-operative evaluation (BMI = Body Mass Index; ROM = Range of Motion, SD Standard Deviation)

Table 3 Average angles calculated according to the Knee Society total knee arthroplasty roentgenographic evaluation and scoring system

5. Conclusions

Funding

Author contributions

Ethics statement

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Baseline characteristics and clinical pre/intra-operative evaluation (BMI $=$ Body Mass Index; ROM $=$ Range of Motion, SD Standard Deviation)

Table 3
Average angles calculated according to the Knee Society total knee arthroplasty roentgenographic evaluation and scoring system