REVIEW 4 major objections 5 minor 25 references
Estimating 2D Keypoints of Surgical Tools Using Vision-Language Models with Low-Rank Adaptation
T0 review · 4 major / 5 minor · reviewed 2026-08-05 · deepseek-v4-flash
Pith's one-line read With two epochs of LoRA fine-tuning, Qwen2.5-VL-3B predicts surgical-tool keypoints at MPJPE 0.0627 and PCK@0.10 0.8908, beating YOLOv8-Pose and SurgeoNet.
desk verdict A plausible transfer of the LoRA-VLM keypoint recipe to surgical tools, but the headline 'outperforms' claim is built on a single test-set-selected run and a 0.0024 MPJPE gap. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing mechanism is the pairing of a frozen pretrained vision-language model with Low-Rank Adaptation (LoRA): only two small matrices per transformer attention projection are trained, so the model keeps its pretrained visual-semantic knowledge while learning the surgical keypoint vocabulary. On top of this sits the prompt-based visual question-answering formulation, which converts 12 numeric (x,y) coordinates into a token sequence; the standard causal language-modeling loss then teaches the model to produce tool names and coordinates jointly. The LoRA rank controls how much task-specific capacity is injected, and the paper identifies rank 8 (with scaling factor 16) as the point whe
What would settle it
Fine-tune the same model with random visual weights (same architecture, no pretraining) under the identical LoRA recipe; if MPJPE stays near 0.0627, the localization is coming from the training loss rather than the pretrained representation, and if it jumps toward the no-fine-tune level (~0.43), pretraining is essential. A second check: evaluate on an instrument type held out from the 14 SurgeoNet classes—if PCK collapses, the adapters are memorizing tools instead of generalizing keypoint structure.
Extended reading notes
Core claim
The central claim is that vision-language models, lightly adapted with LoRA, can perform structured spatial localization—estimating 12 semantic 2D keypoints across 14 surgical instrument types—at a level comparable to or better than dedicated CNN and transformer detectors. The paper demonstrates this by reformulating keypoint detection as prompt-conditioned text generation: the model receives an RGB image plus a fixed prompt asking for the tool name and 12 keypoints, and is trained with a standard causal language-modeling loss to output the coordinates token by token. On the SurgeoNet test set, the LoRA fine-tuned Qwen2.5-VL-3B achieves MPJPE 0.0627 and PCK@0.10 0.8908, improving on YOLOv8-P
Load-bearing premise
The frozen VLM already holds enough visual and spatial knowledge that a rank-8 LoRA update, trained for just two epochs on text-formatted coordinates, can convert that knowledge into accurate, consistent surgical-tool keypoints.
Editorial extensions
If this is right
- If the result holds, small annotated medical datasets no longer require training a large detector from scratch; a frozen VLM plus a two-epoch, low-rank update can reach keypoint accuracy competitive with specialized models.
- Because the same prompt-and-coordinate format is used for every tool type, extending the pipeline to new instruments or to hand-tool joint keypoints is largely a matter of enlarging the instruction dataset.
- The rank ablation implies that under a fixed short schedule, the adapter capacity—not the base model alone—controls whether the localization task is learned; rank 8 is a stable operating point for similar dense spatial prediction tasks.
- Fine-tuned VLMs remain competitive even when trained for far fewer epochs than the CNN/transformer baselines, suggesting the main cost shifts from training compute to prompt and data construction.
Reading between the lines
- The paper does not isolate where the localization signal comes from; a natural test would be to freeze the visual encoder and train only the language-side LoRA head, or to swap in a randomly initialized visual backbone, to see whether the pretrained visual features are actually the source of the gain.
- Because the un-fine-tuned models score near zero PCK, the two epochs of LoRA are evidently creating the keypoint mapping rather than merely 'unlocking' an existing one; the paper's framing that pretraining 'harnesses generalization' is therefore an interpretation, not yet demonstrated by ablation.
- The text-coordinate output may impose a precision ceiling tied to the tokenizer's numeric representation; a head-to-head against a same-backbone regression or heatmap head would show whether VLM tokenization is the limiting factor or a free lunch.
- A sharper practical test is cross-domain evaluation on the SurgeoNet split: fine-tune on synthetic images and evaluate on real captures (or held-out instrument types) to see whether the VLM's pretraining actually narrows the synthetic-to-real gap, which the paper's aggregate numbers do not reveal.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a VLM-based pipeline for 2D keypoint estimation of surgical tools. The task is reformulated as visual question answering: given an image and the prompt “What is/are this/these tool(s) and find 12 keypoints?”, a VLM fine-tuned with LoRA outputs the tool name and 12 numeric (x,y) keypoints. Experiments on the SurgeoNet dataset compare Qwen2.5-VL-3B and DeepSeek-VL2-tiny with LoRA against YOLOv8-Pose and SurgeoNet. The main empirical claim is that after only two epochs of LoRA fine-tuning, Qwen2.5-VL-3B achieves MPJPE 0.0627 and PCK@0.10 0.8908, outperforming YOLOv8-Pose (0.0672, 0.8466) and SurgeoNet (0.0651, 0.8519). A rank ablation on the same test set selects rank 8 as the best configuration. The discussion concludes that VLMs with lightweight adaptation can be competitive for structured localization tasks.
Significance. If the empirical claim is robust, the result is noteworthy: it would show that a frozen pretrained VLM can be adapted with a small number of trainable parameters (20.7M of 3.78B) to perform dense, structured 2D keypoint localization at a level comparable to dedicated CNN/Transformer pose estimators, using only a token-level language modeling loss and no heatmap or regression head. The paper also provides a useful comparison of two VLM families and a LoRA-rank ablation. The manuscript’s strengths include evaluation on a public dataset, comparison to strong baselines, and a simple, conceptually clear pipeline. However, the central “outperforms” claim currently rests on a single unseeded run with a hyperparameter chosen on the test set, so the stated margins cannot be distinguished from run-to-run noise.
major comments (4)
- [Table 2 and Table 1] The headline improvement of Qwen2.5-VL-3B over SurgeoNet is 0.0024 MPJPE (0.0627 vs 0.0651) and over YOLOv8-Pose is 0.0045. Rank 8 was selected by an ablation on the same test set used for the final evaluation, and no validation split or repeated runs are reported. With a 3B-parameter model trained for two epochs with a stochastic objective, these margins are within plausible run-to-run variance. The paper should either report mean±std over multiple seeds, or choose LoRA rank on a validation split and evaluate only once on the test set. Without this, the specific “outperforms” claim in the abstract is not secure.
- [Section 4 (Evaluation Metrics and Dataset)] The manuscript does not specify how keypoint coordinates are normalized or serialized into text, nor how images containing more than one tool are handled. The prompt asks about “this/these tool(s)” and the dataset contains “one or more surgical tools,” but the evaluation pipeline is not described for multi-tool images. The normalization factor L in Eq. (4) and the image resolution/coordinate scaling used in Eq. (3) are also unspecified. These details are needed for independent reproduction of the reported numbers; without them the exact experimental protocol is ambiguous.
- [Section 4 (Experimental Setup) and Section 3 (Eq. 2)] The paper reports only “two epochs” for the VLM and “more than 100 epochs” for baselines, but omits essential training details: optimizer, learning rate, batch size, sequence length, LoRA target modules (beyond “all attention projections and optionally feed-forward”), and whether the language modeling loss is the only objective. Since the central empirical result depends on the LoRA-fine-tuned model’s convergence behavior, the lack of these details, together with the absence of any seed or variance analysis, makes the result difficult to evaluate or reproduce.
- [Abstract and Section 5 (Discussion)] The abstract states that “the adapted VLM outperforms the baseline models,” but Table 1 shows that DeepSeek-VL2 (fine-tuned) does not outperform YOLOv8-Pose or SurgeoNet on PCK and has higher MPJPE than SurgeoNet. Only the Qwen model outperforms both baselines on all metrics. The conclusion in Section 5 more cautiously says the method “reached a comparable level,” which is inconsistent with the abstract. The claim should be scoped to the specific model and metrics, or the abstract should be revised.
minor comments (5)
- [Title/Keywords] Typos and formatting issues: “T able” in Table 1, “perforamnce” in Section 4, and inconsistent whitespace around equations. Please proofread.
- [Conclusions] The conclusion states “We designed tailored prompts and reconstructed a synthetic dataset,” but the experiments section says the authors used the SurgeoNet dataset. Clarify whether a synthetic dataset was reconstructed and, if so, how it differs from the original SurgeoNet data.
- [Figure 1 and Figure 2] The figures are referenced in the text but not described in enough detail. Figure 2 especially is a generic LoRA diagram; consider removing or making it concrete to the architecture used.
- [References] Some references have formatting issues (e.g., Ref. 16 “arXiv preprint arXiv 2411.06869” is missing a colon/dot). Also, since the paper compares against SurgeoNet, more detail on the original SurgeoNet protocol (stereo vs monocular) would help contextualize the “monocular camera” qualification in Table 1.
- [Section 4 (Ablation Study)] The ablation claims rank 16 “may lead to suboptimal convergence or mild overfitting,” but no training curves or convergence analysis are provided. Either support this claim or soften it.
Circularity Check
No significant circularity: predictions are supervised outputs trained and tested on the public SurgeoNet data against external baselines.
full rationale
The paper's derivation chain is straightforward supervised learning: the VLM is fine-tuned with LoRA on SurgeoNet training images using a causal language-modeling loss over serialized keypoint coordinates, and is then evaluated on the SurgeoNet test set against external baselines (YOLOv8-Pose, SurgeoNet). No equation in the paper defines a predicted quantity in terms of a fitted constant, no claimed 'prediction' is derived from the same data used to fit it in a way that forces the result, and no load-bearing argument reduces to a self-citation. The only notable methodological weakness is that the LoRA rank ablation in Table 2 uses the test set to select rank 8, which is evaluation bias and may make the reported 'outperforms' claim less secure, but it is not circularity: the final MPJPE/PCK values are still genuine outputs of a trained model on held-out test images. The self-citation in related work ([25], a survey co-authored by one of the present authors) is not load-bearing. Therefore no circular step can be quoted, and the appropriate score is 0.
Assumptions & free parameters
free parameters (4)
- LoRA rank r =
8
- LoRA scaling factor alpha =
16
- LoRA dropout =
0.05
- Fine-tuning epochs =
2
assumptions (4)
- domain assumption SurgeoNet ground-truth 12 keypoints correctly label the same semantic tool parts across all 14 instrument types and train/test splits.
- domain assumption Causal language modeling loss over generated coordinate tokens provides a valid training signal for spatial localization.
- domain assumption Pretrained VLM representations transfer to surgical instruments after low-rank adaptation.
- domain assumption Baseline comparisons use fair, fixed evaluation code and comparable data preprocessing.
Cite this review
Pith. "Pith review of Estimating 2D Keypoints of Surgical Tools Using Vision-Language Models with Low-Rank Adaptation." pith.science (2026). https://pith.science/paper/7A6FLWGL
@misc{pith2026250820830,
author = {Pith},
title = {Pith review of: Estimating 2D Keypoints of Surgical Tools Using Vision-Language Models with Low-Rank Adaptation},
year = {2026},
howpublished = {\url{https://pith.science/paper/7A6FLWGL}},
note = {Machine review of arXiv:2508.20830}
}
read the original abstract
This paper presents a novel pipeline for 2D keypoint estima- tion of surgical tools by leveraging Vision Language Models (VLMs) fine- tuned using a low rank adjusting (LoRA) technique. Unlike traditional Convolutional Neural Network (CNN) or Transformer-based approaches, which often suffer from overfitting in small-scale medical datasets, our method harnesses the generalization capabilities of pre-trained VLMs. We carefully design prompts to create an instruction-tuning dataset and use them to align visual features with semantic keypoint descriptions. Experimental results show that with only two epochs of fine tuning, the adapted VLM outperforms the baseline models, demonstrating the ef- fectiveness of LoRA in low-resource scenarios. This approach not only improves keypoint detection performance, but also paves the way for future work in 3D surgical hands and tools pose estimation.
Figures
Figures from the paper (2 more)
Reference graph
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Reviewed August 5, 2026 · model on record in the stance chip above.
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