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Indian Journal of Orthopaedics logoLink to Indian Journal of Orthopaedics
. 2025 Feb 21;59(3):414–425. doi: 10.1007/s43465-025-01343-3

Modified Macroscopic Soft Tissue Injury (Modified MASTI) Classification for Bone and Soft Tissue Integrity in Cruciate Retaining Total Knee Arthroplasty

Ravikumar Mukartihal 1,✉, Rajdeep Das 1, Sharan Shivaraj Patil 1, Vikram G K Bhat 1, S Chandan 1, Ratnakar Vecham 2, A V Gurava Reddy 2, Adarsh Annapareddy 2
PMCID: PMC11973035  PMID: 40201926

Abstract

Background

The purpose of this study was to develop a ‘modified macroscopic soft tissue injury (MASTI) classification’ for cruciate retaining (CR) total knee arthroplasty (TKA), and compare the iatrogenic injury of robotic-arm assisted (RA) TKA and conventional jig-based (CJ) TKA using it.

Methods

100 symptomatic knee osteoarthritis patients were chosen of which fifty received RA TKA, whereas fifty received CJ TKA. Posterior cruciate ligament (PCL), soft tissue envelope and bone resection surfaces were assessed during operation and scores allotted for each. The overall score was then graded to form the classification.

Results

The classification had a high inter-observer reliability. RA TKA patients had significantly better PCL scores, soft tissue injury scores, bony injury scores, and modified MASTI grades, and had decreased chances and extent of soft tissue release for coronal balancing. Lesser degree of constitutional varus and sagittal plane deformity, and lower BMI have been found to be associated with better soft tissue preservation and better-modified MASTI grades.

Conclusion

The ‘modified MASTI classification’ is a validated and reliable system to serve as a universal tool and platform for recording and grading iatrogenic bone and soft tissue injury during CR TKA. Using this classification, RA TKA is found to be less invasive and inflicts lesser extent of iatrogenic injuries when compared to CJ TKA. This classification can also be used as a parameter for evaluating the outcome of bone and soft tissue injuries and soft tissue releases to short- and long-term functional outcomes of patients, complications and longevity of implants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43465-025-01343-3.

Keywords: Total knee arthroplasty, Total knee replacement, Soft tissue injury, Classification

Introduction

Conservation of the periarticular soft tissue covering in total knee arthroplasty (TKA) with avoidance and mitigation of iatrogenic injuries to soft tissue structures is of paramount importance to favorably affect rehabilitation, and clinical and functional outcomes [1, 2]. Intraoperative component alignment and positioning, soft tissue balancing and joint laxity are significantly related with pain outcomes in TKA, irrespective of the choice of technology [3, 4]. Literature attests better or tantamount protection of bone and soft tissues during robotic-arm assisted (RA) TKA in comparison to manual conventional jig-based (CJ) TKA [2, 5, 6]. Significant minimization of periarticular soft tissue release and repeat bone resections, prevention of iatrogenic injuries, with satisfactory attainment of gap balance and joint laxity is predominantly contributing to better functional and patient-reported outcomes, which is reflected in patients returning to their previous activity levels with lesser ‘consciousness’ of the operated knee at one, two, and five years post-TKA for RA TKA compared to CJ TKA [7, 8]. Even for constrained implants, robotic technology has shown significant improvement in clinical outcomes at short-term follow-up [9]. And it has been proven that for RA TKA, functional alignment obtains significantly better balance in extension, medially and overall than mechanical alignment [10]. Even with restricted kinematically aligned TKA, RA TKA can more accurately restitute native anatomy and coronal alignment of the knee, as compared to CJ TKA. [11]

Kayani et al. [6] have formulated Macroscopic Soft Tissue Injury (MASTI) classification as a standard and structured guide to systematically and structurally report bone and soft tissue trauma that might be incurred during total knee arthroplasties (TKAs). It is the sole classification system devised till date for grading periarticular injuries during TKAs [6]. However, the classification is applicable only for Cruciate Sacrificing TKA [6]. Hence, the purpose of our study was development of a ‘modified MASTI classification’ for gradation of iatrogenic periarticular bone and soft tissue injury happening during cruciate retaining (CR) TKAs as there is no such classification till date in existing literature.

The objectives of this study were:

  1. Development of a ‘modified MASTI classification’ and check of its validity for analysis of intra-operative bone and soft tissue injury in CR TKA;

  2. Comparison of the injury between RA TKA and CJ TKA using the modified classification;

  3. Correlation of the modified MASTI grading with baseline variables obtained from the study.

The hypothesis of this study was that RA TKA would have better soft tissue and bone protection in comparison to CJ TKA by modified MASTI classification score and grade.

Materials and Methods

Study Population

This was a prospective study done on fifty consecutive patients who had received CJ TKA operation and fifty consecutive patients who had received RA TKA operation, over a period of six months. This study was carried out in accordance with the STROBE guidelines across two tertiary level orthopedic hospitals. All the operations were done by the most experienced chief surgeons of the hospitals, trained well in and routinely performing both CJ TKAs and RA TKAs. Intra-operative assessment was done and scores were allocated by three fellowship trained surgeons, not performing the surgical procedure. The three surgeons individually assessed and allocated the scores of the soft tissue and bone surface intraoperatively, after balancing was complete in flexion and extension, and before placement of implant.

The inclusion criteria had included:

  1. Symptomatic clinically and radiologically proven knee primary osteoarthritis,

  2. Kellgren–Lawrence (KL) classification Grades 3 and 4,

  3. Varus deformity of the knee,

  4. Age ≥ 45 years,

  5. Patient willing and suitable for primary CR TKA,

  6. Consent to take part in the study.

The exclusion criteria had included:

  1. Inflammatory arthropathies,

  2. Post-traumatic or post-infective arthritis,

  3. Collagen disorders,

  4. Any previous extra-articular or intra-articular trauma or surgical procedure to the affected knee.

The suitability for operation was decided by a team of doctors sought for pre-surgical evaluation by the surgeons and anesthetists.

Preoperative Data

The baseline characteristics with regard to gender, age, body mass index (BMI), incidence of comorbidities, American Society of Anesthesiologists Physical Status (ASA-PS) comorbidity class, flexion range, degree of varus deformity, KL osteoarthritis grading, knee side, and native coronal or sagittal plane deformities and their correctability were noted for all the patients. The preoperative assessment and the planning were done with plain radiographs of both knees in antero-posterior, lateral and skyline views, along with a weight bearing lower limb scannogram. Patients who underwent RA TKAs additionally had undergone a preoperative computed tomography scannogram of both lower limbs. All the preoperative assessments and the planning were finalized by the chief surgeon operating on the patient.

Operative Procedure

TKAs were undertaken with standard pre-operative, intra-operative, and post-operative analgesia and anesthesia protocols. After tourniquet application, anterior midline skin incision and standard medial parapatellar approach were used. Principle of ‘adjusted’ or ‘modified’ mechanical alignment, i.e., to mildly under-correct the constitutional coronal varus alignment by preserving some varus (3–5 degrees) alignment after TKA [12, 13], with gap balancing technique was adhered to for CJ TKA. Principle of ‘functional alignment’ [14], i.e., by manipulating alignment, bony cuts, implant positioning, and/or soft tissue releases intra-operatively by robotic-assisted systems for attaining balanced flexion–extension gaps and ligamentous tension, while maintaining patient’s joint line obliquity by minimal release and maximum protection of soft tissue envelope, with ligament balancing workflow (pre-resection balancing workflow) was adhered to for RA TKA. Patella was everted, but native patella was preserved in all cases. Soft tissue protection was done with Mikhail retractors and Posterior Cruciate Ligament (PCL) was protected with PCL retractor. Selective soft tissue releases were performed only when deemed necessary after performing the bony cuts within the safe zone limits, for satisfactory flexion and extension gaps, patellar tracking, and implant stability during arc of motion. The PCL status was noted before placement of implant.

Stryker Triathlon © ® (Stryker, Mahwah, NJ) implant system was used, comprising a Stryker Cruciate Retaining femoral component, Stryker Triathlon X3 Tibial insert and Stryker Triathlon Primary Tibial base plate. MAKOplasty© ™ TKA system (software version 1.0) was used for RA TKA.

Modified MASTI Classification

Soft Tissue Injury Score

The knee was divided into four zones: anterior, posterior, medial, and lateral zone (Fig. 1). Medial and lateral zones were divided with a parasagittal plane passing posteriorly from PCL through the most pronounced part of tuberosity of tibia (shown by red line in Fig. 1). Anterior zone included the extensor mechanism: quadriceps tendon, patella with patellar tendon, whereas posterior zone included PCL and posterior capsule. All the four zones were macroscopically examined intra-operatively for soft tissue injuries (Fig. 2).

Fig. 1.

Fig. 1

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Schematic presentation of the four zones of the modified MASTI classification on the tibial plateau

Fig. 2.

Fig. 2

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A representative intraoperative picture of the soft tissue structures of all four zones and PCL after balancing and before implant placement. The PCL score and the modified MASTI score were allocated by the surgeons during this stage of operation

Soft tissue appearances were graded into six categories, and each zone was allotted a score based on the most severe/worst soft tissue injury in the zone. The scores for each zone were:

  1. Intact soft tissue: ten,

  2. Controlled soft tissue release (planned releases without any adjacent damage): eight (Fig. 3a),

  3. Soft tissue contusion (superficial involvement without any deep layer involvement): seven (Fig. 3b),

  4. Soft tissue fibrillation (macroscopic fraying or maceration of deep layers of soft tissue): five (Fig. 3c),

  5. Soft tissue cleavage (partial to complete soft tissue damage-cut or transaction, except for the collateral ligaments, quadriceps or patellar tendon): three (Fig. 3d),

  6. Unintentional soft tissue detachment (any extent of injury to collateral ligaments, quadriceps or patellar tendon): zero for all four zones.

Fig. 3.

Fig. 3

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a A representative intraoperative picture, where the yellow arrow shows planned medial soft tissue release (eight score) and the gray arrow shows some PCL contusion (eight score). b A representative intraoperative picture, where the orange arrow shows soft tissue contusion (seven score) and the green arrow shows PCL fibrillation of < 50% area (seven score). c A representative intraoperative picture, where the red arrow shows soft tissue fibrillation (five score) and the gray arrow shows some PCL contusion (eight score). d A representative intraoperative picture, where the purple arrow shows soft tissue cleavage (three score) and the white arrow shows PCL fibrillation of > 50% area (five score)

PCL Score

We allocated a separate PCL score in the ‘modified MASTI classification’. PCL injury was specified as its fibers being contused, cut, torn, fretted, macerated, avulsed, or transected. For determining the extent of injury, the surface area of injured portion was divided by the total surface area of PCL. The points allocated were:

  1. Uninvolved PCL: ten,

  2. PCL contusion: eight (Fig. 3a),

  3. PCL fibrillation (macroscopic incomplete damage-cut, frayed, macerated) < 50% affected: seven (Fig. 3b),

  4. PCL fibrillation ≥ 50% affected: five (Fig. 3d),

  5. Partial PCL avulsion/ transection: three,

  6. Unintentional PCL avulsion/ transection: zero for all four zones.

Modified MASTI Soft Tissue Grade

A summation of the soft tissue score of four zones and PCL score was done for the final modified MASTI soft tissue score, which was then stratified into five distinct grades: 1- excellent, 2- good, 3- average, 4- poor, and 5- defunctioned knee (Table 1). We classified the score into five grades in contrast to four groups in the original MASTI classification.

Table 1.

Modified macroscopic soft tissue injury (modified MASTI) classification

Grade Description Score Description
1 Excellent  ≥ 44 No iatrogenic injury/iatrogenic injury to any 1 zone with relative soft tissue preservation of the other zones
2 Good 36– < 44 Minimal iatrogenic injury to ≥ 2 zones with relative soft tissue preservation of the other zones
3 Average 27– ≤ 35 Significant iatrogenic injury to ≥ 2 zones with relative soft tissue preservation of the other zones
4 Poor  ≤ 26 Significant iatrogenic soft tissue injury to ≥ 3 zones with injury of the PCL
5 Defunctioned knee 0 Injury to superficial MCL ± LCL ± extensor mechanism (quadriceps tendon, patella, patellar tendon) ± Complete PCL avulsion/ transection defunctioning knee, irrespective of the soft tissue appearance in any other zone
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Bone Injury Score

The final macroscopic appearance of resected bone surfaces of most injured part of femur and tibia after balancing the knee and before implant placement was assessed to evaluate bone injury score. Grade I implied that surface preparations were smooth and clean after bony resections (Fig. 4). Grade II implied that bony resections were spotted or uneven due to injury inflicted during preparation of the surfaces (Fig. 4). Grade III implied that multiple bony resections were required for acceptable preparation of the bone surfaces or that bony wedges were needed for restoring joint line. Importantly, we did not consider bony re-cuts done for optimizing balancing to downgrade bone injury score.

Fig. 4.

Fig. 4

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A representative intraoperative picture of the bone resection surfaces of the femur and tibia after the final bony cuts, and before implant placement. The black arrow shows smooth and clean femur bone surface, which is allocated as Grade I. The blue arrow shows spotted tibia bone surface, which is allocated as Grade II

Data Analysis

All the data were compiled with Microsoft Excel 2016 and analyzed using IBM SPSS (Version 27). Qualitative variables were presented as number of patients, percentages, and mode with range. Quantitative variables were presented as ratios, means, and standard deviations. Data analysis tests and tools used in the study included: chi-square test of Fischer exact test, 2-sample proportion test, independent samples t test, and binary logistic regression analysis. Pearson’s correlation coefficient was used for measuring interclass correlation. A classification tree analysis model was utilized to predict the modified MASTI score grading using the baseline characteristics of patients. P value of < 0.05 was considered significant.

Results

Baseline Variables of the Patients

The RA TKA and CJ TKA patients were similar with respect to patients’ baseline variables with no significant difference (Table 2).

Table 2.

Characteristics of the baseline variables of the CJ TKA and RA TKA patients

Variable CJ TKA (n = 50) RA TKA (n = 50) P-value
Gender (men/women) 21/29 18/32 0.539
Age (mean ± SD) 63.32 ± 8.86 64.24 ± 13.70 0.691
Body mass index (BMI) (mean ± SD) 28.46 ± 4.12 27.29 ± 4.12 0.156
Comorbidity (yes/no):
 1. Hypothyroidism 12/38 7/43 0.202
 2. Asthma 3/47 3/47 1.000
 3. Seizure 3/47 1/49 0.307
 4. Hypertension 27/23 30/20 0.545
 5. Coronary artery disease 2/48 3/47 0.646
 6. Diabetes mellitus 14/36 19/31 0.288
 7. Hepatitis B infection 2/48 2/48 1.000
Side affected (right/left) 26/24 25/25 0.841
Coronal deformity (°) (mean ± SD) 5.58 ± 3.02 6.14 ± 2.77 0.336
Correctable coronal deformity (yes/no) 26/24 22/28 0.423
Sagittal deformity (°) (mean ± SD) 4.06 ± 4.41 3.44 ± 3.79 0.453
Correctable sagittal deformity (yes/no) 37/13 36/14 0.822
ASA-PS class (mode, range) 2 (2–3) 2 (2–3) 1.000
Flexion range (°) (mean ± SD) 100.90 ± 8.37 102.90 ± 6.78 0.192
Varus (°) (mean ± SD) 8.44 ± 4.27 7.98 ± 3.88 0.574
X-ray KL classification (mode, range) 3 (3–4) 3 (3–4) 1.000
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Modified MASTI Soft Tissue Score and PCL Score

RA TKA patients had highly significantly better overall modified MASTI soft tissue scores and mean PCL scores in comparison with CJ TKA patients (Table 3). There was no requirement for any form of PCL release in cases of RA TKA.

Table 3.

Comparison of the mean PCL score and mean modified MASTI soft tissue score between CJ TKA and RA TKA patients

Mean score CJ TKA (n = 50) RA TKA (n = 50) P-value
Soft tissue score (mean ± SD) 39.87 ± 5.16 45.23 ± 5.47  < 0.001
PCL score (mean ± SD) 8.67 ± 1.37 9.31 ± 0.97 0.009
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Inter-observer Correlation

There was a substantial inter-observer agreement, with ICC (inter-class correlation coefficient): 0.995 (95% confidence interval: 0.993–0.996, P value < 0.001) for soft tissue scores and 0.938 (95% Confidence interval: 0.913–0.956, P value < 0.001) for PCL scores of the ‘modified MASTI classification’.

Modified MASTI Soft Tissue Grade

RA TKA patients had significantly more grade 1 scores (P < 0.01) and fewer grade 2 scores (P < 0.01), with no difference in grade 3 scores (P > 0.05), in comparison to CJ TKA patients. There was no grade 4 or 5 score in any group (Table 4). Odds ratio indicated that RA TKA patients were 3.9 times more likely to get grade 1 score than CJ TKA patients (P < 0.01, 95% CI 1.69–9.15).

Table 4.

Comparison of the modified MASTI soft tissue grades between CJ TKA and RA TKA patients

Modified MASTI soft tissue grade CJ TKA (n = 50) RA TKA (n = 50) P-value
1 13 29 0.003
2 29 14
3 8 7
4 0 0
5 0 0
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Modified MASTI Bone Injury Score

RA TKA patients had significantly more grade I femur bone scores (P < 0.05) and fewer grade II femur bone scores. Odds ratio indicated RA TKA patients were 1.86 times more likely to get grade I score than CJ TKA (P < 0.05, 95% CI 1.04–3.32). No patient received Grade III femur bone score in either group. Similarly, RA TKA patients had significantly more grade I tibia bone scores (P < 0.05) and fewer grade II tibia bone scores (P < 0.05). The two groups had no difference for grade III tibia bone score (Table 5).

Table 5.

Comparison of the modified MASTI bone injury grades between CJ TKA and RA TKA patients

Bone Injury Grade CJ-TKA (n = 50) RA-TKA (n = 50) P-value
Femur I 30 41 0.027
II 20 9
III 0 0
Tibia I 28 38 0.107
II 20 11
III 2 1
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Soft Tissue Release for Coronal and Sagittal Balancing

For coronal balancing, RA TKA patients had significantly increased proportion of patients who required no soft tissue release (P < 0.01) and less posteromedial release (P < 0.01). Odds ratio suggested that CJ TKA patients were 2.44 times more likely to have a posteromedial release compared to RA TKA patients. Importantly, RA TKA patients were 53 times more likely to have no soft tissue release compared to CJ TKA patients. The two groups had no difference with respect to soft tissue release for sagittal release (Table 6).

Table 6.

Comparison of the soft tissue release required for coronal balancing and sagittal balancing between CJ TKA and RA TKA patients

Soft tissue release for coronal balancing CJ TKA (n = 50) RA TKA (n = 50) P-value
No soft tissue release required 00 26  < 0.001
Deep medial collateral ligament (MCL) Release < 50% 06 09
Deep MCL release > 50% 12 06
Posteromedial release 22 09
Superficial MCL release 04 00
Medial tibial reduction osteotomy 06 00
Soft tissue release for sagittal balancing CJ TKA (n = 50) RA TKA (n = 50) P-value
No soft tissue release required 41 45 0.452
Posterior capsule release 06 04
Additional distal femur cut 03 01
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The various types of soft tissue release that were done for coronal and sagittal balancing during CR TKA are illustrated in the table

Discussion

The most important feature of this study was the development of a novel ‘modified MASTI classification’, that is a validated tool for recording intraoperative bone and soft tissue injuries during CR TKA. The ‘modified MASTI classification’ is graded into five soft tissue grades based on the severity of soft tissue injury and three bone grades based on pristineness of bony resections. The important findings include that the RA TKA patients had significantly better modified MASTI soft tissue and bone grades as compared to CJ TKA patients. RA TKA patients required significantly less soft tissue release compared to CJ TKA patients.

CR implants have the minimum constraint, and hence their outcome is profoundly linked with the biomechanical periarticular environment. It necessitates fine bony surfaces, nominal defects, undamaged soft tissues, and intact, functionally balanced PCL [15]. The integrity of periarticular soft tissue envelope is of utmost importance for successful patient-reported outcomes, proper functioning and longevity of CR TKAs [16]. However, iatrogenic injuries to ligaments and surrounding structures, such as ligamentous instability, ligamentous disruption, patellar tendon ruptures, patellar eversion, extensor mechanism disruption, tibio-femoral or patello-femoral dislocation, patellar fractures and peroneal nerve injury, have been reported in literature, which inadvertently and invariably leads to complications and failures [17–25]. Literature is still sparse for evidence to properly analyze the iatrogenic soft tissue and ligamentous injury happening during RA TKAs or CJ TKAs, and their comparative evaluation [26]. There is no such literature till date for CR TKAs. Kayani et al. [6] developed a structured and systematic grading system for reporting and grading of iatrogenic bone and soft tissue injuries in cruciate sacrificing implants, which they coined as the MASTI classification. It is the only classification system available till date in literature for cruciate sacrificing TKA [6]. Hence, we have developed a ‘modified MASTI classification’ for its use in CR TKA- both for RA TKA as well as CJ TKA. The ‘modified MASTI classification’ is the first classification in literature which provides structured and systematic grading of bone and soft tissue injury in CR TKA.

Iatrogenic soft tissue injury from saw blade happens when the manually controlled oscillating saw crosses the bony limits and breaches soft tissue. The hand-held oscillating saw significantly crosses bone edges even in hands of skilled surgeons [27]. Although neurovascular complications are rarely reported, direct breach in knee capsule and surrounding soft tissue envelope can result from manually controlled oscillating saw blade during bone resections [26]. Bone resections in RA TKA are executed with an oscillating saw by auditory, visual, and tactile feedback. The robotic-arm guided saw blade remains operational strictly within the predefined stereotactic boundary limits [6]. The stereotactic perimeter which is created and projected by the robot depends upon component geometry, osseous anatomy based on the preoperative CT scan and minimum gaps required for saw blade oscillation [24]. Even newer imageless robotic systems have also demonstrated high level of accuracy to execute the bone cuts and angles [28]. But although there is an enhanced capacity to achieve precise intraoperative bone resections in terms of coronal and sagittal plane alignments with RA TKA, there is a potential lack to sense the periarticular soft tissue structures [24, 29]. Hence, the chances for bone and soft tissue injury in spite of a stereotactic boundary in RA TKA should necessarily be systematically evaluated [24]. A recent systematic review by Nogalo et al. [25] advised caution for orthopedic surgeons of RA TKA during bone cuts for averting iatrogenic injuries. In this study, we found that the incidence of iatrogenic bone and soft tissue trauma is reduced significantly by the stereotactic perimeter in RA TKA, which is reflected with better modified MASTI bone and soft tissue scores and grades of RA TKA in comparison with CJ TKA.

Functionally deficient PCL and non-resilient degenerate PCL are contraindications for CR TKA [30]. Many surprising scenarios arise when conversion to posterior stabilized (PS) TKA is intraoperatively determined for unanticipated factors. It is of paramount importance to recognize those factors which might require conversion to PS TKA. In CR TKA, the foremost task is to assess the macroscopic appearance and the elasticity of the PCL. A native PCL score of ≤ 5 suggests degenerative PCL which may be functionally compromised. Such patients might be poor candidate for CR TKA and PS implants becomes the modality of choice from the beginning in such patients [30]. Further, during CR TKAs, manual resection of tibia had been linked with PCL injury in 45% to 69% cases intraoperatively [31, 32]. Intraoperative PCL injury causes balancing mismatch, with considerably increased flexion gap than extension gap, and more lateral flexion gap than medial flexion gap [33]. This results in medio-lateral flexion instability resulting in short to midterm CR implant failures, and in many cases, may effect intraoperative conversion from CR to PS implants [30, 34]. Although Kayani et al. [6] included posterior zone in their classification, PCL was not assessed in their study as they had used PS implants. This creates a potential lacuna as PCL is a very important structure for CR implants. This study introduces the classification of PCL score to overcome this gap. Intraoperatively, if the PCL score is found to be ≤ 3, then PCL is poorly elastic and compromised, and needs conversion to PS TKA. Thus, we conclude that the native PCL score as well as intraoperative PCL score of the ‘modified MASTI classification’ can aid in decision-making of patients as to who shall be poor candidates for CR TKA and might need conversion to PS TKA. Moreover, we have also found that RA TKAs have significantly better PCL scores than CJ TKAs. This can be correlated with the PCL perimeter of stereotactic boundary for the tibia cut in CR RA TKAs that helps to protect the PCL.

In RA TKAs, the component placement and ligament balancing can be checked intraoperatively and intraoperative resections and alignments can be quantified and achieved with significant precision, which minimizes the chance of occurrence of a significant instability [29, 35]. The bone cuts can be manipulated and modified intra-operatively by changing resection depths, rotational alignments, size, and position of implants based on live on-screen changes to obtain desired component placement and gap balancing with no or minimum soft tissue releases [2, 6]. We have also utilized this to modify bony resections in the necessary planes so that the soft tissue release is either not necessary or minimally required. In this study, it is supported by the fact that RA TKAs have lower proportion of soft tissue releases as compared to CJ TKAs, which is significant for coronal soft tissue balancing but not significant for sagittal soft tissue balancing. The ability to change depths, alignments, and angles of the bone resections in RA TKAs intra-operatively before the actual cuts minimizes the chances of repeated bone resections. The real-time color code of the bone during resection process, which depends on how much bone has been cut, displays the error in bone resections and helps in real time to prevent further damages. All these lead to better bone injury scores in RA TKAs as compared to CJ TKAs in this study. The reduced need for soft tissue release and repeated bony resections in RA TKA proves advantageous in early postoperative period, with studies documenting lesser opioid requirements, shorter length of stay, and lesser physiotherapy sittings, when compared with CJ TKA [36]. At the same time, no differences in post-operative hemoglobin drop, readmission or reoperation rate, complications, range of motion and Patient-Reported Outcome Measures were noted between image-based/imageless RA TKA and CJ TKA [37, 38]. O’Rourke et al. in their national database study concluded that RA TKA might even be linked with lesser inpatient complication rates compared to CJ TKA candidates [39].

Prior deformity of the knee and BMI influences the need for soft tissue release in TKA, with greater deformities and higher BMI needing more soft tissue release [40]. Our findings also indicate that lower degree of constitutional varus and lower BMI are associated with lesser degree of soft tissue release, reflecting with better modified MASTI grades. Additionally, lower degree of constitutional sagittal plane deformity of the knee is also found to be associated with better grades.

Heightened anxiousness, mental tension, and physical strain during the initial learning phase of RA TKA correlate with inferior surgeon performance, substandard decisions, and diminished skills of the surgical team [25]. This could be a significant factor for chance of more iatrogenic injuries during this phase. Schopper et al. [41] have shown that a robotic-assisted system trained surgeon in RA TKA could flatten the learning curve of a robotic-assisted system inexperienced operating team. Whether the presence of such an experienced surgeon could possibly lead to decrease in iatrogenic bone and soft tissue injuries is something to look forward to and analyze using ‘modified MASTI classification’.

Mahure et al. observed a learning curve phase of 10 to 20 cases for active robotic TKA [42]. The learning curve renders an in-depth analysis of the system safety and adoptability as well as complications which might occur or should be anticipated during the phase [42]. The ‘modified MASTI classification’ can also be aptly implemented for active robotic TKA systems to analyze the iatrogenic injuries during the learning curve of active robotic systems as iatrogenic injuries are more common in active robotic systems [25].

Limitations

The modified MASTI score does not take into account the degree of injury of individual structures of each zone separately; hence, it underscores the degree of injury of a knee which suffers injuries to multiple structures within one zone. The study was not blinded because during score assessment, the RA TKA knees had bone pins, arrays assembly and bone check points attached to femur and tibia, and did not have intramedullary drill hole in femur, as opposed to CJ TKA knees, which had intramedullary drill hole in femur. The clinical relevance of the modified MASTI classification in post-operative inflammation, post-operative pain and analgesia, hemoglobin drop, functional rehabilitation, physiotherapy settings, length of hospital stay, and long-term clinical and functional outcomes and longevity of implants has not been evaluated in this study.

Conclusion

The ‘modified MASTI classification’ is the first structured classification and grading system in the literature developed for CR TKA by ascertainment of bone and soft tissue injury intra-operatively. It has high inter-observer validity. Hence, it can be reliably used as a universal tool for detailed, standardized, and uniform reporting of iatrogenic bone and soft tissue integrity during CR TKAs. Robotic-assisted TKAs have been found to have significantly lesser extent and severity of bone and soft tissue injuries as compared to conventional jig-based TKAs, using the ‘modified MASTI classification’. Lesser degree of constitutional varus and sagittal plane deformity, and lower BMI have been found to be associated with better soft tissue preservation and better modified MASTI grades. The classification can also serve as a platform for comparison of data regarding the amount of soft tissue releases performed during CR TKAs, which has not been possible previously. It can also be used as a parameter for correlation of the extent or severity of bone and soft tissue injuries to postoperative outcomes like post-operative inflammation, post-operative pain and analgesia, hemoglobin drop, physiotherapy sittings, length of hospital stay and other factors affecting rehabilitation and long-term functional outcome of patients, complications, and longevity of implants. This definitely creates a potential scope of future research with the use of this classification.

Supplementary Information

Below is the link to the electronic supplementary material.

Supplementary file1 (19KB, docx)

Acknowledgements

Dr. Babar Kayani for grant of permission to work upon the original MASTI classification and develop its modification for use in Cruciate Retaining Total Knee Arthroplasty. K. Soujanya Wilson, Manager –Clinical Research, PhD Clinical Sciences, Sparsh Group of Hospitals, Bangalore, Karnataka, India.

Abbreviations

MASTI

Macroscopic soft tissue injury

CR

Cruciate retaining

TKA

Total knee arthroplasty

RA

Robotic arm-assisted

CJ

Conventional jig-based

PCL

Posterior cruciate ligament

TKAs

Total knee arthroplasties

STROBE

Strengthening the reporting of observational studies in epidemiology

KL

Kellgren–Lawrence

ICC

Inter-class correlation coefficient

BMI

Body mass index

ASA-PS

American Society of Anesthesiologists Physical Status

CI

Confidence interval

MCL

Medial collateral ligament

PS

Posterior stabilized

Author Contributions

R. M: conceptualization, methodology, software, validation, formal analysis, investigation, resources, data curation, writing—review and editing, visualization, supervision, project administration. R. D: conceptualization, methodology, software, validation, formal analysis, investigation, resources, data curation, writing—original draft, writing—review and editing, visualization, project administration. S. S. P: methodology, validation, formal analysis, investigation, resources, data curation, writing—review and editing, visualization, supervision, project administration. V. G. K. B: methodology, formal analysis, investigation, resources, data curation, writing—original draft, writing—review and editing, visualization, supervision. C. S: methodology, formal analysis, investigation, resources, data curation, writing-original draft, writing—review and editing, visualization, supervision. R. V: validation, formal analysis, investigation, resources, data curation, writing—review and editing, visualization, supervision, project administration. A. V. G. R: validation, formal analysis, investigation, resources, data curation, writing—review and editing, visualization, supervision, project administration. A. A: validation, formal analysis, investigation, resources, data curation, writing—review and editing, visualization, supervision, project administration.

Funding

The authors declare that no funds, grants, or other support was received during the preparation of this manuscript.

Declarations

Conflict of Interest

The authors have no relevant financial or non-financial interests to disclose.

Ethical Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Patient Consent

Informed written consent had been obtained from all individual participants included in the study.

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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