A novel precision micro-drilling technique for treating osteochondral lesions of the talus with superior cartilage regeneration and early rehabilitation compared with microfracture: a randomized controlled study with 2-year follow-up

Abstract

Background

Arthroscopic microfracture (MF) is currently the most widely used surgical treatment for osteochondral lesions of the talus (OLTs), but poor cartilage regeneration and prolonged rehabilitation are the focus of improvement. This study aimed to conduct a novel procedure, subtle and precise osteo-drilling for the recovery of talus (SPORT surgery) with self-designed instruments and compare its clinical outcomes to the MF for OLTs. The novel procedure has the potential to address certain limitations of MF, including the significant subchondral bone destruction and restricted drilling position.

Study design

Randomized controlled trial; Level of evidence, 1.

Methods

A total of 56 patients with OLTs who underwent surgical treatment from September 2021 to August 2022 were randomly assigned to the MF group or the SPORT group. For the SPORT group, a novel high elastic K-wire with a 1.2 mm diameter was used to drill subchondral bone holes with 10 mm depth through a curved guide. Clinical assessments were conducted by using VAS (Visual Analog Scale), AOFAS (American Orthopaedic Foot & Ankle Society) score, FAAM-ADL (Foot and Ankle Ability Measure-Activities of Daily Living) score, and SP (Foot and Ankle Ability Measure-Sports) score. MRI evaluation included relative signal intensity of subchondral bone marrow edema (RSI-SBME), volume of the subchondral bone marrow edema (V-SBME), and the Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) score. The differences in clinical outcomes and imaging results between the two groups were compared at pre-surgery, postoperative 3, 6, 12, and 24 months.

Results

Both the MF and SPORT groups showed significant improvement in all clinical outcomes. At 3- and 6-month post-op, the clinical outcomes of the SPORT group were significantly better than those of the MF group (improved 44.6 % and 32.2 % at 3- and 6-month postoperative for FAAM-SP, P ≤ 0.001). The percentage of patients in the SPORT group who met the MCID of FAAM-SP is significantly higher than in the MF group at 3-month (P = 0.007) and 6-month (P = 0.005) postoperative. Besides, the SPORT group achieved better MOCART scores than the MF group at all follow-ups (P ≤ 0.002). After 12 months, there was no significant difference in clinical outcomes between the two groups.

Conclusion

The novel device-guided SPORT surgery has significant advantages over conventional MF technology in terms of early postoperative return to sport and long-term cartilage regeneration in OLT patients.

The translational potential of this article

The SPORT surgery and the novel guided subchondral bone drilling instruments have excellent translational potential in sports medicine as an alternative to replace traditional MF techniques for OLTs and can be extended to cartilage repair in other joints, such as the knee and shoulder.

Graphical abstract

1. Introduction

Ankle sprains are one of the most common diseases in orthopedic emergencies, with a prevalence of 7 %–12 % among athletes [1]. Osteochondral lesions of the talus (OLTs) are found in about 50 % of ankle sprains and are related to factors including mechanical abnormalities, cartilage wear, local ischemia, and metabolic abnormalities from acute sprains or chronic ankle instability [[2], [3], [4]]. OLTs mainly manifest as diffuse ankle joint dull pain that worsens during weight-bearing and physical activity. Some patients may also experience symptoms such as swelling and joint locking, which can severely impact quality of life and athletic performance. Untreated OLTs can lead to extensive cystic changes, accelerate joint degeneration, and even cause talus necrosis and disability [5,6]. Therefore, timely treatment is necessary to prevent the progression of chronic injury. Since the avascular structure and poor self-healing capacity of cartilage, surgical treatments are commonly required, which generally include bone marrow stimulation, osteochondral transplantation, and chondrocyte implantation [[7], [8], [9], [10], [11]].

Bone marrow stimulation (BMS), which is recommended for small OLTs management, is to induce the formation of fibrocartilage at the lesions by subchondral drilling or microfracture (MF) on the subchondral bone, allowing the migration of blood and mesenchymal stem cells [[12], [13], [14], [15], [16]]. Transmalleolar drilling and MF were reported to have comparable surgical results, and MF was thought as a preference for its capacity to reach posterior medial or posterior lateral OLTs without iatrogenic injury and severe postoperative subchondral bone marrow edema (SBME) [[17], [18], [19]]. However, patients undergoing traditional BMS were reported to experience slow symptom improvement in the early post-op period, and the long-term efficacy was also concerning due to the poor quality of fibrocartilage [[20], [21], [22], [23]]. According to previous studies, the average time for return to sport in OLT patients undergoing MF may be as long as approximately 6 months postoperatively [24]. The reason might be due to that the traditional microfracture uses the hammer with strong strikes and shakes, which will cause subchondral bone destruction, especially in the case of incomplete bone plates or poor bone quality, resulting in poor cartilage repair results [25]. At the same time, the limited drilling depth (3–4 mm) does not allow the pressure of the subchondral bone to be fully released, which is also considered to be an important cause of pain in OLTs [26]. According to our previous studies, the drilling depth was preferable to the subchondral 5- to 10-mm depth [27]. The subchondral drilling surgery results in more regular holes, less damage to the subchondral bone and deeper drilling depths, which is conducive to decompression and the release of blood from the bone marrow. However, for most OLTs that are hard to reach because of their location on the talar dome, K-wire would be directed across the medial malleolus into the lesion, which causes the disruption of the tibial cartilage [28,29].

In the present study, a novel procedure, subtle and precise osteo-drilling for the recovery of talus (SPORT surgery), was conducted with novel surgical instruments, including the core being curved-tip guides and scaled high elastic K-wire. Compared to MF, SPORT surgery causes less destruction of the subchondral bone and forms deeper holes, which is beneficial for the decompression of the subchondral bone and the release of stem cells from the bone marrow [26]. Through instrument design and material processing, our modified K-wire, with a curved tip, can rotate and drill more than 50 times at a 10 mm depth without fracture or excessive vibration, thereby greatly extending the talar regions accessible to subchondral drilling. Thus, drilling can be performed without damaging the tibia while precisely controlling the position and depth of the drilling, which is a difficult problem to solve in transmalleolar drilling [2,29] (Fig. 1). A total of 56 patients with OLTs were involved and randomized to two groups (conventional MF and SPORT surgery). The clinical and radiological outcomes were evaluated at pre-surgery and postoperative 3, 6,12 and 24 months. We hypothesized that the SPORT surgery could achieve faster rehabilitation with earlier sports recovery and superior cartilage regeneration. This new technique and instruments have a good translational potential for the surgical treatment of OLTs as well as the potential to be extended to the treatment of other articular cartilage injury. (e.g., knee and shoulder).

Fig. 1.

Comparison of advantages and disadvantages of microfracture, transmalleolar drilling, and subtle and precise osteo-drilling for the recovery of talus (SPORT surgery).

2. Materials and methods

2.1. Study design

This was a prospective, randomized, parallel, controlled study conducted at our single institution. This study was approved by the Clinical Research Ethics Committee of Peking University Third Hospital (IRB00006761-M2021178). This study has been registered with the Chinese Clinical Trial Registration Center (ChiCTR2100051851). Patients were eligible for inclusion in this randomized controlled trial if they needed BMS with symptomatic OLTs at the Peking University Third Hospital between September 2021 and August 2022. All subjects recruited were randomly divided into two groups by a random table: the intervention group (SPORT group) and a control group (MF group). A sample size calculation was performed a priori based on the FAAM-SP at 6 months from a previous pilot study. To establish a clinically significant mean difference of 10.7 points with the standard deviation of two groups were 12.3 and 12.6 (0–100 scale) respectively, A total of 18 patients was needed in each group considering 80 % power and an alpha level of 0.05. To account a potential dropout rate of approximately 20 %, we sought to include a total of 25 patients in each group. Actually, we eventually included 28 patients in each group. All patients gave their written informed consent before enrollment in the study.

2.2. Inclusion and exclusion criteria

Inclusion criteria included: (1) aged between 18 and 60; (2) focal ankle discomfort symptoms, which can be aggravated by exercise, and conservative treatment for 3 months has no obvious improvement; (3) the diameter of OLTs smaller than 10 mm, the size of OLTs smaller than 100 mm², and the depth of OLTs smaller than 5 mm under arthroscopic measurement; (4) Those who can understand this study and sign the informed consent. Based on previous studies, OLTs larger than 100 mm² or those associated with large cysts (which usually increase lesion depth to larger than 5 mm) have a low success rate with BMS and generally require more aggressive treatments such as autologous osteochondral transplantation or autologous osteoperiosteal transplantation [30,31]. Therefore, these patients were not included in the present study.

Exclusion criteria: The excluded patients were those combined with large cystic OLTs, co-existing tumors, infectious diseases, ankle arthritis (evaluated as grade III or IV based on Takakura-Tanaka classification), history of surgeries, or other neuromuscular diseases in the same lower extremity [32,33].

2.3. Randomization procedure

Firstly, the randomization coordinator used SPSS software (Version 24.0; SPSS, Inc) to generate 56 random numbers ranging from 0 to 1 and sequentially numbered from 1 to 56. Based on a 1:1 allocation ratio, the 28 subjects with the smaller values were assigned to the MF group, and the 28 subjects with the larger values were assigned to the SPORT group. To ensure allocation concealment, 56 opaque, sealed envelopes were used and numbered from 1 to 56. The randomization coordinator placed the two surgical methods into the corresponding numbered envelopes and placed them in the operation room. Investigating physicians were to evaluate possibly eligible patients and obtain informed consent. After completing the above steps, the surgeon would perform an arthroscopic examination to assess the OLTs. Once it was confirmed that the patient fully met the criteria, the research nurse would open the envelope placed in the operating room, which was signed with the same number as the patient's enrollment sequence, to determine the surgical method (Fig. 2).

Fig. 2.

Flowchart of this study.

2.4. Surgical technique

All surgeries were performed by the same senior surgeon under spinal lumber anesthesia. Patients lay supine with the ipsilateral hip lifted around 30^° by a pillow. A tourniquet was tied at the root of the thigh with a pressure of 300 mmHg. Routine anteromedial and anterolateral portals were first made, and diagnostic arthroscopy was executed under 2.9 mm 30^° arthroscope instruments (Smith & Nephew, Andover, MA). OLTs were confirmed, debrided, and assessed. After the surgical method was determined, MF or SPORT surgery was performed. MF was performed by an arthroscopic awl as a routine way, and the MF holes were made at 3–4 mm intervals with 3 mm depth. SPORT surgery was performed using the forementioned specialized instruments. Depending on the lesion location, the curved-tip guide was inserted through either a medial or lateral approach, supplemented by an anteromedial approach if necessary. The guide's tip was adjusted to be perpendicular to the debride OLTs. Under arthroscopic visualization, the 1.2 mm drilling pin was inserted through the guide to the OLTs. The tail of the pin was connected to a surgical drill, and the drilling depth from the subchondral bone surface was controlled to 10 mm according to the scale change on the tail of the pin. The drill speed was carefully managed to ensure slow penetration. After each drilling, the pin was removed under arthroscopy monitoring, and then adjusted the curved-tip guide to the next drilling site which was 3–4 mm away from the previous one. This process was repeated to create subsequent channels (Fig. 3). After the BMS finished, suitable bone bleeding and marrow fat droplets were confirmed by releasing the tourniquet before closing the wound. Concomitant modified Broström surgery was performed to repair the lateral ankle ligament for those with chronic ankle instability.

Fig. 3.

Novel surgical instruments were used in ankle arthroscopic surgery. (A) The curved- and straight-tip guides and high elastic K-wire. (B) The high elastic K-wire does not show significant deformation after a large-angle bend. (C–D) Under arthroscopy, the guide and K-wire were used to drill holes at different angles for the precision drilling of the lesion. (E) Close-up of the scale of the guide during drilling.

2.5. Rehabilitation

Patients followed a standard rehabilitation protocol, including continuous passive motion starting on post-op day 3, partial weight-bearing starting after 4 weeks post-op, and complete weight-bearing began at week 6 with an ankle walking brace. Muscle strength and balance exercises were also performed. At weeks 8–12, patients were allowed to do activities according to their tolerance. An identical postoperative rehabilitation protocol was applied to patients in both groups.

2.6. Evaluation of clinical outcome

A clinician who was blinded to the treatment performed all clinical assessments. The visual analog scale (VAS) was used to quantify the level of pain numerically. The general function was evaluated by the American Orthopaedic Foot & Ankle Society Ankle and Hindfoot scores (AOFAS) and Foot and Ankle Ability Measure Activities of Daily Living Subscale (FAAM-ADL) [34,35]. Sports activity levels were evaluated by the Foot and Ankle Ability Measure Sports Subscale (FAAM-SP) [35]. All clinical evaluations were conducted at 5 time points as pre-surgery, 3, 6, 12, and 24 months post-op. Clinical outcomes at 3 and 6 months post-op would be used for the evaluation of early rehabilitation and return to sport as the primary end-point. The minimal clinically important differences (MCIDs) of the VAS score and AOFAS score were 2 points and 29 points, according to the published literature [36,37]. As for FAAM scales, including FAAM-ADL and FAAM-SP, the MCIDs were 8 and 17.2 points, respectively [36].

2.7. MRI measurement

MRI was performed at the affected ankle in a neutral position using a Signa HDxt 3.0-T MRI system (GE Healthcare, Chicago, IL) with an 8-channel ankle joint surface coil at 5 time points as pre-surgery, 3-, 6-, 12-, and 24-month post-op. Two senior foot and ankle surgeons blinded to the treatment independently measured all images. The SBME and Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) were evaluated [38]. The SBME was measured at the proton density (PD) spin-echo scans in coronal and sagittal images (Echo time: 30–45 ms; Repetition time: 2500–3500 ms), including its signal intensity and volume. The relative signal intensity of SBME (RSI-SBME) was defined as the ratio of the average grey value of SBME at the largest area of SBME in the coronal image to the grey value of the surrounding normal subchondral bone. The volume of SBME (V-SBME) was evaluated by the ellipsoid formula as previously introduced [39]. The mean value of the two measures was used for subsequent analyses. If the MOCART scores were different, the measurers would discuss to agreement.

2.8. Statistical analysis

All statistical analyses were performed by IBM SPSS Statistics 27 (IBM Corp., Armonk, NY, USA). Mean ± standard deviation (SD) was used to express all quantitative data unless otherwise specified. Characteristics and clinical information data (including age, sex, BMI, the location of the lesion, lesion size, presence of cysts, and concomitant surgeries), clinical results (including VAS, AOFAS, FAAM-ADL and FAAM-SP scores) and the MRI measurement results (including V-SBME, RSI-SBME, and MOCART) were all analyzed. The reliability of the measurement for RSI- and V-SBME was evaluated by calculating intraclass correlation coefficients (ICCs). The one-way repeated-measures general linear model (GLM) with a Sidak test for multiple comparisons was performed to evaluate the changes over time. The comparison of results between the two groups was analyzed by the independent sample t-test or the Mann–Whitney U test based on normality tests. Furthermore, to prove the clinical significance of the difference, an analysis of MCIDs was conducted by the chi-square test. Bivariate associations between the patient characteristics and primary end-points (FAAM-SP at 3- and 6-month postoperative) were assessed with Pearson correlation coefficients (r): strong correlation, |r| = 0.5–1.0; moderate, |r| = 0.3–0.5; weak, |r| = 0.1–0.3. A p-value of <0.05 was considered statistically significant.

3. Results

3.1. Baseline data

A total of 56 patients were included and operated between September 2021 to August 2022 and received the allocated interventions. There were no baseline differences between the MF and SPORT groups regarding demographic data, clinical outcomes, perioperative findings, or self-reported outcome scores (Table 1). Both the ICC values for RSI-SBME (0.804, 95 %CI 0.160–0.930, P < 0.001) and V-SBME (0.853, 95 % CI 0.699–0.923, P < 0.001) showed good reliability.

Table 1.

Baseline patient data.

	MF (n = 28)	SPORT (n = 28)	P value
Age, y	36.93 ± 8.12	35.71 ± 7.94	0.574
sex, female/male, n	6/22	4/24	0.727
BMI, Kg/m2	25.06 ± 3.46	24.47 ± 3.12	0.506
Side, L/R	10/18	15/13	0.179
Lesion location (medial/lateral)	20/8	22/6	0.537
Lesion size (mm2)	58.68 ± 26.07	63.59 ± 25.17	0.598
Uncontained lesion, n(%)	17(60.7 %)	17(60.7 %)	1.000
Cystic lesion. n(%)	19(67.9 %)	16(57.1 %)	0.408
Concomitant procedure, (Yes/No)	21/7	21/7	1.000
Number of drill holes, n	2.93 ± 0.98	3.07 ± 1.02	0.594

BMI, Body mass index; MF, microfracture; SPORT, subtle and precise osteo-drilling for the recovery of talus.

3.2. Changes in the clinical and MRI results in each group over time

All clinical outcomes in both the MF and SPORT groups showed significant improvement over time. Both groups demonstrated significant improvements in VAS scores, AOFAS scores and FAAM-ADL scores (P ≤ 0.001) with GLM for repeated measures across five timepoints. A significant difference was found in the SPORT group for MOCART scores (P = 0.004), and no significant changes over time were observed in RSI-SBME or V-SBME scores for either group (Table 2).

Table 2.

Comparison of results over time.

		MF (n = 28)	SPORT (n = 28)
VAS	P: time	<0.001a	<0.001a
AOFAS	P: time	<0.001a	<0.001a
FAAM-ADL	P: time	<0.001a	<0.001a
FAAM-SP	P: time	<0.001a	<0.001a
RSI-SBME	P: time	0.477	0.136
V-SBME	P: time	0.391	0.319
MOCART	P: time	0.088	0.004a

^aRepresents significant difference. AOFAS, the American Orthopaedic Foot & Ankle Society Ankle and Hindfoot scores; FAAM-ADL, Foot and Ankle Ability Measure Activities of Daily Living Subscale; FAAM-SP, Foot and Ankle Ability Measure Sports Subscale; MF, microfracture; MOCART, Magnetic Resonance Observation of Cartilage Repair Tissue; RSI-SBME, the relative signal intensity of subchondral bone marrow edema; SPORT, subtle and precise osteo-drilling for the recovery of talus; VAS, the visual analog scale; V-SBME, the volume of subchondral bone marrow edema.

3.3. Comparison between the MF group and the SPORT group

All preoperative evaluation items showed no differences between the MF group and SPORT group, including VAS, AOFAS, FAAM-ADL, FAAM-SP, RSI-SBME, and V-SBME. At 3-month post-op, the SPORT group demonstrated significantly better outcomes compared to the MF group in terms of VAS scores (P = 0.012), AOFAS scores (P = 0.009), FAAM-ADL scores (P = 0.018), FAAM-SP scores (P = 0.001), and MOCART scores (P = 0.002). At 6-month post-op, the SPORT group continued to show significantly better AOFAS scores (P = 0.008), FAAM-ADL scores (P = 0.006), FAAM-SP scores (P < 0.001), and MOCART scores (P < 0.001) compared to the MF group. However, at 12- and 24-month post-op, there were no significant differences between the two groups in any outcomes except for the MOCART score, which remained significantly better in the SPORT group (P < 0.001) (Table 3, Fig. 4). According to the MCID analysis, no significant differences between groups were observed for the percentage of patients who achieved the MCID postoperatively in all clinical scores except FAAM-SP (Table 4). For the MCID of FAAM-SP, the percentage of patients in the SPORT group who met the MCID is significantly higher than in the MF group at 3-month (P = 0.007) and 6-month (P = 0.005) postoperative. None of these patients in either group developed any postoperative complications, such as wound complications, neural injury or nonunion of osteotomy.

Table 3.

Comparison of outcomes between the MF and SPORT group.

	MF (n = 28)	SPORT (n = 28)	P value
VAS
Preoperative	6.75 ± 1.51	6.79 ± 1.50	0.899
3-month post-op	3.82 ± 1.19	3.04 ± 0.96	0.012a
6-month post-op	2.50 ± 1.04	2.07 ± 0.86	0.079
12-month post-op	1.54 ± 0.92	1.46 ± 1.20	0.741
24-month post-op	1.39 ± 1.32	1.11 ± 1.47	0.200
AOFAS
Preoperative	61.89 ± 9.78	61.36 ± 7.41	0.663
3-month post-op	71.96 ± 8.53	77.25 ± 5.89	0.009a
6-month post-op	78.50 ± 9.44	84.00 ± 4.21	0.008a
12-month post-op	83.50 ± 8.37	86.82 ± 4.64	0.073
24-month post-op	86.89 ± 8.52	90.04 ± 8.05	0.122
FAAM-ADL
Preoperative	62.29 ± 7.78	63.69 ± 9.80	0.516
3-month post-op	72.53 ± 12.79	79.21 ± 9.56	0.018a
6-month post-op	78.91 ± 9.89	85.20 ± 5.84	0.006a
12-month post-op	86.22 ± 8.03	89.75 ± 5.47	0.061
24-month post-op	88.75 ± 7.96	91.33 ± 7.58	0.181
FAAM-SP
Preoperative	38.14 ± 17.25	35.33 ± 16.28	0.534
3-month post-op	29.72 ± 13.75	42.98 ± 13.17	0.001a
6-month post-op	41.20 ± 14.17	54.46 ± 12.62	<0.001a
12-month post-op	53.44 ± 14.85	60.97 ± 16.49	0.078
24-month post-op	59.04 ± 16.70	61.35 ± 16.24	0.748
RSI-SBME
Preoperative	2.84 ± 1.59	3.20 ± 1.67	0.755
3-month post-op	2.77 ± 0.91	2.44 ± 0.97	0.129
6-month post-op	2.59 ± 1.08	2.56 ± 0.97	0.914
12-month post-op	2.98 ± 1.40	2.63 ± 1.29	0.577
24-month post-op	2.51 ± 1.22	2.48 ± 1.15	0.919
V-SBME (mm2)
Preoperative	691.25 ± 1179.87	711.37 ± 680.02	0.127
3-month post-op	731.45 ± 671.17	811.02 ± 692.59	0.611
6-month post-op	660.97 ± 674.46	717.63 ± 988.97	0.762
12-month post-op	902.11 ± 1424.99	731.67 ± 1275.14	0.857
24-month post-op	512.19 ± 686.73	450.19 ± 488.53	0.961
MOCART
3-month post-op	48.39 ± 16.78	60.89 ± 10.81	0.002a
6-month post-op	52.86 ± 14.11	64.64 ± 11.05	<0.001a
12-month post-op	50.00 ± 13.68	65.18 ± 12.80	<0.001a
24-month post-op	56.25 ± 12.74	70.18 ± 12.51	<0.001a

^aRepresents significant difference. AOFAS, the American Orthopaedic Foot & Ankle Society Ankle and Hindfoot scores; FAAM-ADL, Foot and Ankle Ability Measure Activities of Daily Living Subscale; FAAM-SP, Foot and Ankle Ability Measure Sports Subscale; MF, microfracture; MOCART, Magnetic Resonance Observation of Cartilage Repair Tissue; RSI-SBME, the relative signal intensity of subchondral bone marrow edema; SPORT, subtle and precise osteo-drilling for the recovery of talus; VAS, the visual analog scale; V-SBME, the volume of subchondral bone marrow edema.

Fig. 4.

The comparison of the outcomes between the MF group and the SPORT group at each time point. The average is represented by the horizontal line. The interquartile range (IQR) is represented by the box. Median ±1.5 ∗ IQR is indicated by whiskers. MF, microfracture; SPORT, subtle and precise osteo-drilling for the recovery of talus; VAS, the visual analog scale. AOFAS, the American Orthopaedic Foot & Ankle Society Ankle and Hindfoot scores; FAAM-ADL, Foot and Ankle Ability Measure Activities of Daily Living Subscale; FAAM-SP, Foot and Ankle Ability Measure Sports Subscale; MOCART, Magnetic Resonance Observation of Cartilage Repair Tissue. ∗ Represents p < 0.05; ∗∗ Represents p < 0.01; ∗∗∗ Represents p < 0.001.

Table 4.

MCID analysis of outcome measures between the MF and SPORT group.

	Δ(Postoperative score–Preoperative score) ≥ MCID, n (%)		P value
	MF (n = 28)	SPORT (n = 28)
VAS
3-month post-op	19 (67.9 %)	23 (82.1 %)	0.217
6-month post-op	24 (85.7 %)	25 (89.3 %)	0.686
12-month post-op	26 (92.9 %)	27 (96.4 %)	0.549
24-month post-op	26 (92.9 %)	26 (92.9 %)	1.000
AOFAS
3-month post-op	2 (7.1 %)	0 (0.0 %)	0.092
6-month post-op	4 (14.3 %)	5 (17.9 %)	0.716
12-month post-op	6 (21.4 %)	10 (35.7 %)	0.237
24-month post-op	11 (39.3 %)	13 (46.4 %)	0.589
FAAM-ADL
3-month post-op	20 (71.4 %)	23 (82.1 %)	0.342
6-month post-op	25 (89.3 %)	27 (96.4 %)	0.289
12-month post-op	25 (89.3 %)	27 (96.4 %)	0.289
24-month post-op	26 (92.9 %)	26 (92.9 %)	1.000
FAAM-SP
3-month post-op	1 (3.6 %)	8 (28.6 %)	0.007a
6-month post-op	5 (17.9 %)	15 (53.6 %)	0.005a
12-month post-op	13 (46.4 %)	19 (67.9 %)	0.105
24-month post-op	14 (50.0 %)	19 (67.9 %)	0.174

^aRepresents significant difference. AOFAS, the American Orthopaedic Foot & Ankle Society Ankle and Hindfoot scores; FAAM-ADL, Foot and Ankle Ability Measure Activities of Daily Living Subscale; FAAM-SP, Foot and Ankle Ability Measure Sports Subscale; MCID, minimal clinically important difference; MF, microfracture; SPORT, subtle and precise osteo-drilling for the recovery of talus; VAS, the visual analog scale.

3.4. Correlation analysis between patient demographics and clinical outcomes

According to the correlation analysis results at 3-month post-op, the area, depth, and presence of cysts had a moderate correlation with FAAM-SP scores in the MF group. In the SPORT group, a moderate correlation was found only between BMI and FAAM-SP scores. At 6-month post-op, there was no correlation between the presence of cysts and scores, while the remaining results were similar to those at 3-month post-op (Table 5).

Table 5.

Correlation between patient characteristics and postoperative FAAM-SP score.

Correlation between patient characteristics and 3-month postoperative FAAM-SP score
	MF (n = 28)		SPORT (n = 28)
	Rank correlation	P value	Rank correlation	P value
Age	−0.192	0.327	−0.115	0.561
BMI	−0.119	0.545	−0.377	0.048a
Area	−0.433	0.021a	0.152	0.440
Depth	−0.434	0.021a	−0.079	0.690
Medial/Lateral (0/1)	0.134	0.495	−0.197	0.314
Cyst (0/1)	−0.387	0.042a	0.128	0.516
Correlation between patient characteristics and 6-month postoperative FAAM-SP score
	MF (n = 28)		SPORT (n = 28)
	Rank correlation	P value	Rank correlation	P value
Age	−0.059	0.767	−0.215	0.272
BMI	−0.151	0.444	−0.374	0.050a
Area	−0.478	0.010a	0.119	0.548
Depth	−0.434	0.021a	−0.103	0.602
Medial/Lateral (0/1)	0.116	0.557	−0.088	0.657
Cyst (0/1)	−0.239	0.221	0.083	0.674

^aRepresents significant difference. BMI, Body mass index; FAAM-SP, Foot and Ankle Ability Measure Sports Subscale; MF, microfracture; SPORT, subtle and precise osteo-drilling for the recovery of talus.

4. Discussion

The most important finding of this study was that patients with OLTs who underwent SPORT surgery had better clinical outcomes at 3-, 6-month post-op compared to those who underwent MF. Patients treated with SPORT surgery experienced faster post-op improvement in clinical symptoms, particularly in terms of enhanced athletic performance. Additionally, the quality of the regenerated cartilage following SPORT surgery was superior to that of MF. In BMS surgery, the novel surgical instruments applied in this study demonstrated great superiority.

Overall, the results of this study suggested that the novel SPORT surgery could provide better clinical outcomes than MF, especially in the early postoperative period. Despite the fact that MF is currently the most popular surgical technique for small OLTs, unsatisfactory short-term post-op results were reported, leading to a delay in patients returning to sports [9,14,[40], [41], [42]]. Choi et al. compared transmalleolar drilling and microfracture and found that both techniques showed similar clinical outcomes for OLTs, which may be because transmalleolar drilling damages the cartilage on the opposite tibial surface, thereby reducing the effectiveness [17]. Additionally, some researchers have used retrograde drilling to treat primary OLTs to protect the subchondral bone plate, but there was no significant improvement in symptoms compared to microfracture [43]. Retrograde drilling is only recommended for subchondral bone cysts with an intact cartilage surface and is not suitable for full-thickness cartilage defects, thus limiting its application scenarios [10]. In SPORT surgery, the damage to the tibia caused by transmalleolar drilling and the severe damage to the subchondral bone plate caused by microfracture is avoided, resulting in reduced edema and better cartilage quality (Fig. 5). The VAS, AOFAS, FAAM-ADL, FAAM-SP scores of patients undergoing SPORT surgery at 3 months and AOFAS, FAAM-ADL, FAAM-SP scores at 6 months were significantly improved compared to MF. In addition, in the SPORT group, the proportion of patients who met MCID at 3 months and 6 months postoperatively was significantly higher than that in the MF group. These results suggest that SPORT surgery has great advantages in promoting early postoperative rehabilitation and reducing patient braking time. Furthermore, the correlation was found between lesion area, lesion depth, presence of cysts and FAAM-SP scores only in the MF group, suggesting SPORT surgery may have broader indications than traditional MF surgery. In addition, the correlation between BMI and clinical scores in the SPORT group may indicate that the SPORT surgery is particularly suitable for patients with a lower BMI. However, these conclusions still require further refined studies in the future to clarify.

Fig. 5.

Preoperative and postoperative proton density-weighted MR images of two groups of cases. (A–C) A 32-year-old male patient underwent SPORT surgery, with decreased and localized edema early postoperatively. (D–F) A 28-year-old male patient underwent MF surgery, with suspicious cystic change and extensive edema under the subchondral bone plate early postoperatively. The extent of bone marrow edema is indicated by red dashed lines. MF, microfracture; SPORT, subtle and precise osteo-drilling for the recovery of talus.

Besides, this study indicated that the quality of cartilage repair tissue generated after SPORT surgery was better than MF (Fig. 6). Poor quality of the repaired tissues after MF has been reported and was one of the key defects of this procedure. Lee et al. conducted a 2-year follow-up and reported the average MOCART was 53.01 for the regenerated cartilage, and another study also reported the MOCART of the regenerated cartilage was 49.4 at 21.8 months follow-up [44,45], which is similar to the results of the present study. On the other hand, the SPORT group reached significantly better MOCART scores than the MF at all post-op time points, indicating better quality of cartilage repair tissue generated by SPORT surgery. It might be due to SPORT surgery could ensure the smoother migration of cells and growth factors and contribute to more effective bone marrow stimulation [46]. According to our previous study, a 10 mm drilling depth maximizes the release of bone marrow blood without severely disrupting the talar blood supply [27]. Additionally, the finer guide and the micro-serrations at its tip ensure drilling stability, thereby avoiding severe damage to the subchondral bone plate and minimizing interference with surrounding healthy tissue. It should also be noted that both MF and SPORT surgery were to make marrow progenitor cells and growth factors migrate to the lesion and differentiate to fibrocartilage to repair the lesion [14,15,47]. This may be the reason why there is no significant difference in the clinical outcome between the two groups in the results of postoperative 12 and 24 months. The biological mechanisms of the results require further basic research.

Fig. 6.

Preoperative and 24 months postoperative proton density-weighted MR images of two groups of cases. (A–B) A 32-year-old male patient underwent SPORT surgery, with an intact subchondral bone plate and high cartilage repair quality. (C–D) A 41-year-old male patient underwent MF surgery, with a thinner subchondral bone plate, extensive edema, and low cartilage repair quality. The patient in SPORT group obtained better cartilage repair quality and MOCART scores, resulting in better clinical outcomes. MF, microfracture; SPORT, subtle and precise osteo-drilling for the recovery of talus; MOCART, Magnetic Resonance Observation of Cartilage Repair Tissue.

Specifically, SPORT surgery, which is based on new surgical instruments, combines the advantages of MF and subchondral drilling and further refines them to promote cartilage repair. First, this novel procedure employs a K-wire improved with new metallic materials and a front-end curved guide, addressing the issue of traditional drilling being unable to reach deep lesions while avoiding tibial injury, which may be associated with higher-grade OLTs [48]. For clinical safety, we routinely use a new K-wire for each operation to ensure it never breaks during the procedure. Second, using target guides with various curvature angles, combined with preoperative MRI guidance, ensures precise control of drilling direction during surgery. Third, the graduated K-wire allows for precise control of drilling depth. Based on our previous studies, we typically use a drilling depth of 10 mm to promote blood release without excessive damage to the vasculature [27]. Fourth, the instrument set is easy to operate, has a low technical threshold, and is conducive to widespread application. The SPORT surgery and the novel guided subchondral bone drilling instruments have excellent translational potential in sports medicine as an alternative to replace traditional MF techniques for OLTs and can be extended to cartilage repair in other joints, such as the knee and shoulder.

To our knowledge, this is the first randomized controlled trial comparing subchondral drilling and MF for the treatment of OLTs. We have applied improved new instruments and a novel surgical technique, demonstrating the superiority of SPORT surgery over MF. SPORT surgery possesses the same simplicity and minimal invasiveness as MF while significantly improving the short-term clinical outcomes for patients postoperatively, which is of great importance in helping patients quickly resume their daily activities and return to sports. Especially for athletes and sports enthusiasts with OLTs, SPORT surgery offers the possibility for them to return to sports rapidly after surgery, showing a promising outlook for clinical translation. In addition, SPORT surgery has the same safety as MF, without increasing the risk of infection and prolonging the operation time.

This study has several limitations. First, although the sample size requirements are met, the sample size is still relatively small, and other factors such as injury location and cyst are not taken into account. A more detailed subgroup analysis may be needed to confirm the efficacy of SPORT surgery. Second, the follow-up period is short, necessitating further long-term studies to determine the sustained efficacy of the two bone marrow stimulation techniques. Future studies could enhance the evaluation of patients undergoing SPORT and MF to more comprehensively explore the reasons for the different short-term clinical outcomes observed between the two procedures. This approach would help elucidate the mechanisms and identify the optimal drilling technique and distribution characteristics.

5. Conclusion

The novel device-guided SPORT surgery has significant advantages over conventional MF technology in terms of early postoperative return to sport and long-term cartilage regeneration in OLT patients. The novel SPORT technology and device showed good clinical efficacy and safety, and had strong clinical translation potential.

CRediT authorship contribution statement

Yubin Li: Writing – original draft, Methodology, Investigation, Formal analysis, Conceptualization. Xiaoze Fan: Investigation, Data curation, Conceptualization. Dingyu Wang: Investigation, Methodology, Formal analysis. Tong Su: Visualization, Formal analysis, Data curation. Xiangyun Cheng: Formal analysis, Data curation. Jiaxin Liu: Formal analysis, Methodology. Ziming Liu: Funding acquisition, Conceptualization. Dong Jiang: Writing – review & editing, Validation, Supervision, Project administration, Funding acquisition, Resources.

Declaration of Generative AI in scientific writing

During the preparation of this work, the author(s) did not use generative AI.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Funding

The author(s) report funding from Natural Science Foundation of Beijing (L222064), Capital's Funds for Health Improvement and Research (2022-2Z-40913) and Clinical Cohort Construction Program of Peking University Third Hospital (BYSYDL2022016).

Declaration of competing interest

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.